In line external mukuni DF62 fuel pump verses internal carburetor fuel pump for a GP 1200.

[Radical Riche]

What signal is this that you keep referring to the fuel pump sends fuel to the carbs that's its function, and signal is in the carb itself and refers to it's ability to draw fuel into the jets, vacuum is another way to put it, signal can be and I guess in this case is very misleading.
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Brandon from Havasu PWC told me that a external fuel pump won't work on the 1200. Said it sends the wrong signal, my thoughts were it was due to having just one pulse line and not 3, one for each carb to keep each carb pressurized to its matched cylinder. These external fuel pumps are new to me.

 

[WFO Speedracer]

I assure the carbs do not know the difference between three pulses and one, either the fuel pressure is high enough or it isn't, I am not sure how many times or in how many ways this can be stated in this thread, if you want to know for sure check it.

 

[Radical Riche]

I assure the carbs do not know the difference between three pulses and one, either the fuel pressure is high enough or it isn't, I am not sure how many times or in how many ways this can be stated in this thread, if you want to know for sure check it.

Yeah I hear yeah. Wish there was a way to test the fuel pump, engine tore apart.

 

[Radical Riche]

Anyone know the max compression on a GP1200 for 93 pump gas..I was told 160 max. Thanks!

 

[Radical Riche]

I'm using a 1100 case modified to use a 1200 block. It's the same case other than modifying for the 1200 sleeves.

There’s a article group k make about crank torsion where they claim that because the rear most cyl is closest to the pump and furthest from the flywheel that it twists under heavy load and actually advances the timing 2-3 degrees on that cyl.
This generates catastrophic heat and shows up as a lean condition.
Now they claim they have no solid evidence BUT I know the 96? 1100ZXI’s began to pull the ignition timing back on the rear cylinder at certain temps and rpm and I believe Yamaha did the same on the 1200 electronics. Someone who knows more history about sit downs might know better.
Anyways you’ll also see engines like the 64u that have lower rear cyl compression from factory and retard the timing of that cyl.

As far as seals blowing on 1100 cranks I never had that be much of an issue but I have fought the notorious lean rear cyl condition many a time

Is that why the 1200 exhaust manifold gasket has the front 2 cylinders cooling water restricted allowing most of the cooling water to enter into the rear cylinder? I added dual cooling lines with a water outlet on head above the center cylinder.

 

[DylanS]

Anyone know the max compression on a GP1200 for 93 pump gas..I was told 160 max. Thanks!

There are several factors that go into determining octane so without knowing the exact specs of an engine it’s hard to give an accurate number.
I’d say 93 octane is safe to at least 150 psi on a stockish gp1200 engine for WOT pulls.

If I was you, building a 1200 blaster, I would just put the pumps back on the carbs.
Browse the web for someone with similar specs to your build and start your jetting close to where they are.
Take your time and check your temps and plugs. Use a tach if possible.
Take your time and break your engine in properly.
And do NOT let your friends ride the bugger until you’re sure you’ve got it tuned to withstand a thrashing.. learned my lesson on that a few times.

 

[WFO Speedracer]

There are several factors that go into determining octane so without knowing the exact specs of an engine it’s hard to give an accurate number.
I’d say 93 octane is safe to at least 150 psi on a stockish gp1200 engine for WOT pulls.

If I was you, building a 1200 blaster, I would just put the pumps back on the carbs.
Browse the web for someone with similar specs to your build and start your jetting close to where they are.
Take your time and check your temps and plugs. Use a tach if possible.
Take your time and break your engine in properly.
And do NOT let your friends ride the bugger until you’re sure you’ve got it tuned to withstand a thrashing.. learned my lesson on that a few times.

I think he would rather try and invent the wheel at this point.

 

[DylanS]

I think he would rather try and invent the wheel at this point.

Come on WFO be a good mentor and fly out to help the fella build his ski!!!

 

[WFO Speedracer]

The closest I will get to flying is in a hovercraft, so I will have to pass on that one.

 

[Radical Riche]

There are several factors that go into determining octane so without knowing the exact specs of an engine it’s hard to give an accurate number.
I’d say 93 octane is safe to at least 150 psi on a stockish gp1200 engine for WOT pulls.

If I was you, building a 1200 blaster, I would just put the pumps back on the carbs.
Browse the web for someone with similar specs to your build and start your jetting close to where they are.
Take your time and check your temps and plugs. Use a tach if possible.
Take your time and break your engine in properly.
And do NOT let your friends ride the bugger until you’re sure you’ve got it tuned to withstand a thrashing.. learned my lesson on that a few times.

Thanks!

 

[Radical Riche]

I don't like the fact that there is only one pulse line using a external fuel pump. I drilled/tapped to add dual "fuel in" pump lines and one "fuel out" to the 3rd carb. No one seems to know if the mikuni DF62 would be able to pump dual fuel lines. The pump body is marked with a arrow to add both additional lines. Going back to pumps on carbs. Brendan from Havasu PIC said you can't run external fuel pump on 1200s. I'm thinking he's correct

 

[Radical Riche]

I'm lost on the restrictors, I have mikuni 44 BN which are taper bored. I didn't drill and restrictors out of carbs nor do I have any restrictors in my return line. I have a external fuel pump with each having it's own fuel line from the mikuni DF62 fuel pump. I would have to way to monitor fuel pressure guage inside engine compartment on a B1. I'm leaning going back to internal pumps in carbs, I didn't have this problem with the 1100 which lasted 8 years. I had 150 psi compression before I discovered my lean condition. I can hone cylinder, buy new piston and rings and change to 125 pilot and 145 main. But I still think I had a case leak which caused the lean condition. There's fuel wash on top of all 3 pistons so it was dumping the fuel. Thanks for your help!!

My 44 carbs are stock other than Pro tec tapped boring them. Do I need to drill out carb restrictors? If so where are they located? I have block off plates due to deleting internal fuel pumps.

 

[DylanS]

My 44 carbs are stock other than Pro tec tapped boring them. Do I need to drill out carb restrictors? If so where are they located? I have block off plates due to deleting internal fuel pumps.

Internal restrictor is located underneath the fuel pump side plate right next to the return nipple here:


Thread on sizing jet and testing pressure:

importance of the correct return jet sizing

I recently discovered after spending countless hours on here searching for advice and trying every logical jetting combo known to man I started to see a lot of people post issues similar to the problems I was having and struggling to get their ski tuned properly and it always seemed to ended up...

www.x-h2o.com

I think you’re fine on that setup and shouldn’t have much to worry about other than pop off tuning and jetting.

 

[Radical Riche]

Internal restrictor is located underneath the fuel pump side plate right next to the return nipple here:
View attachment 433685

Thread on sizing jet and testing pressure:

importance of the correct return jet sizing

I recently discovered after spending countless hours on here searching for advice and trying every logical jetting combo known to man I started to see a lot of people post issues similar to the problems I was having and struggling to get their ski tuned properly and it always seemed to ended up...

www.x-h2o.com

I think you’re fine on that setup and shouldn’t have much to worry about other than pop off tuning and jetting.

Okay got it. So you are saying that I want to drill the restrictor orfise out? What's the benefit? Is it less pressure on fuel pump which gives better fuel supply? But why add one in the return like..sounds like defeating the purpose. Thanks man!!

 

[Radical Riche]

Internal restrictor is located underneath the fuel pump side plate right next to the return nipple here:
View attachment 433685

Thread on sizing jet and testing pressure:

importance of the correct return jet sizing

I recently discovered after spending countless hours on here searching for advice and trying every logical jetting combo known to man I started to see a lot of people post issues similar to the problems I was having and struggling to get their ski tuned properly and it always seemed to ended up...

www.x-h2o.com

I think you’re fine on that setup and shouldn’t have much to worry about other than pop off tuning and jetting.

Also do you think.the DF 62-702 external fuel pump is better than the carb internal fuel pump?

 

[DylanS]

Okay got it. So you are saying that I want to drill the restrictor orfise out? What's the benefit? Is it less pressure on fuel pump which gives better fuel supply? But why add one in the return like..sounds like defeating the purpose. Thanks man!!

Yes people *carefully* drill them out. The benefit is now you can put a jet inline on the return line and that allows you to adjust your fuel pressure anywhere you’d like by changing jet sizes. Bigger jet less fuel pressure and vise versa.
This becomes necessary on modified engines, big bore and strokers, to compensate for the difference In pulse strength.
For example my 66e 5mm stroker had fuel pressure upwards of 5psi at idle with a 70 return jet. I had to go to a 110 to get my fuel pressure into a normal range and then adjust my jetting. Fuel pressure that high at idle was giving me issues with fuel “dribbling” out of my carbs.


Typically you’ll want to be between 1-2psi at idle and 5-7psi WOT or so I believe.
Lower fuel pressure means less fuel thru jets and vise versa.
You’re most likely completely fine letting your carbs alone.

You will have no issue with either onboard or external pump. I prefer to run onboard pumps for simplicity. You’re over thinking this whole ordeal

 

[Radical Riche]

Yes people *carefully* drill them out. The benefit is now you can put a jet inline on the return line and that allows you to adjust your fuel pressure anywhere you’d like by changing jet sizes. Bigger jet less fuel pressure and vise versa.
This becomes necessary on modified engines, big bore and strokers, to compensate for the difference In pulse strength.
For example my 66e 5mm stroker had fuel pressure upwards of 5psi at idle with a 70 return jet. I had to go to a 110 to get my fuel pressure into a normal range and then adjust my jetting. Fuel pressure that high at idle was giving me issues with fuel “dribbling” out of my carbs.


Typically you’ll want to be between 1-2psi at idle and 5-7psi WOT or so I believe.
Lower fuel pressure means less fuel thru jets and vise versa.
You’re most likely completely fine letting your carbs alone.

You will have no issue with either onboard or external pump. I prefer to run onboard pumps for simplicity. You’re over thinking this whole ordeal

Thanks bro. I just rebuilt engine to a 120p and it lasted 10mins. Had lean condition grated one of rear seal blew out but I had to up jets and n/s etc, got pop off to like 28lbs. In order to change jets I gotta take motor out of hull..got a B1 so trying to cover my bases. I had a 110 pilot and 135 main, was gonna up them to 120 and 145 but was my lean condition due to the ONE seal being blown out? Should i up jets or leave them what they were. This is where I worry. Thanks for your info.

 

[DylanS]

Thanks bro. I just rebuilt engine to a 120p and it lasted 10mins. Had lean condition grated one of rear seal blew out but I had to up jets and n/s etc, got pop off to like 28lbs. In order to change jets I gotta take motor out of hull..got a B1 so trying to cover my bases. I had a 110 pilot and 135 main, was gonna up them to 120 and 145 but was my lean condition due to the ONE seal being blown out? Should i up jets or leave them what they were. This is where I worry. Thanks for your info.

There’s a lot of things that can lead to a failure that have nothing to do with jetting.
If you have pictures of the damage to your rear cyl I’d post them so we can look at them and get an idea on what happened.

Few things that come to mind.
Why did a real seal blow out on a fresh rebuild? Did you tear the entire motor down or did you just do a top end? There could have been debris in the case on that cyl if you didn’t tear the entire motor down.
What were you doing when you blew the rear cyl? If you were WOT on a motor with less than 10 minutes on it that could’ve been a big part of your issue.
Improper installation of parts or improper clearances could’ve been an issue.
Yes a single blown seal can introduce unmetered air into your engine, they put two there for a reason lol.

You need to build this motor properly from the bottom up in a clean environment and do a proper leak down test first and foremost. Then you need to break it in properly and watch your temps and read your plugs until you’re confident in your tuning. It’s pretty hard to melt a rear cyl with semi close jetting if you aren’t going nuts wide open across the lake.
Do some research, it’s impossible for me or anyone to give you a dead nuts jetting spec
and you’ll have to account for your conditions too when basing your jetting off someone else’s similar build.

 

[Radical Riche]

There’s a lot of things that can lead to a failure that have nothing to do with jetting.
If you have pictures of the damage to your rear cyl I’d post them so we can look at them and get an idea on what happened.

Few things that come to mind.
Why did a real seal blow out on a fresh rebuild? Did you tear the entire motor down or did you just do a top end? There could have been debris in the case on that cyl if you didn’t tear the entire motor down.
What were you doing when you blew the rear cyl? If you were WOT on a motor with less than 10 minutes on it that could’ve been a big part of your issue.
Improper installation of parts or improper clearances could’ve been an issue.
Yes a single blown seal can introduce unmetered air into your engine, they put two there for a reason lol.

You need to build this motor properly from the bottom up in a clean environment and do a proper leak down test first and foremost. Then you need to break it in properly and watch your temps and read your plugs until you’re confident in your tuning. It’s pretty hard to melt a rear cyl with semi close jetting if you aren’t going nuts wide open across the lake.
Do some research, it’s impossible for me or anyone to give you a dead nuts jetting spec
and you’ll have to account for your conditions too when basing your jetting off someone else’s similar build.

Tore engine down due to me messing with the carbs in the Fall because it was running rich and had a lean run away. That engine was 8 years old and had cross hatch markes still in cylinder s when I took out engine to install a torrent 155 with Carter b tunnel. Anyhow after the run away I decided to put a 1200 jug on it. Well the mechanic accidently put the rear seals in with the 4 tabs on the inside and it blew out. When I first started engine it went wot and I thought something was wrong. I put it in the river, was tuning the carbs and couldn't get a good color on plugs. Thought I needed to up jets. Ordered new jets and discovered rearseal was out. I changed jetting from my 1100 for the 1200 engine to 110 pilot, 135 main, 25lbs pop off/95 gram spring. I had 150 psi compression before I tore it down. I had fresh bore on cylinder, new piston etc. I blame the seals being installed incorrectly. All 3 cylinders have the same amount of slight scuffag. I'm getting cylinders honed, new piston and rings. Also having head checked. When I tore the head off I noticed a rust ring at the top of all 3 cylinders where rings don't ride. I don't like the 1200 head gasket or manifold gaskets. I was told to put them on dry but pro tec said to use a light coat of permatex red spray. I added a 3/8 cooling line and added the water out fitting behind middle cylinder to help keep it cool. I heard 1200 run hot. I see what machinist

There’s a lot of things that can lead to a failure that have nothing to do with jetting.
If you have pictures of the damage to your rear cyl I’d post them so we can look at them and get an idea on what happened.

Few things that come to mind.
Why did a real seal blow out on a fresh rebuild? Did you tear the entire motor down or did you just do a top end? There could have been debris in the case on that cyl if you didn’t tear the entire motor down.
What were you doing when you blew the rear cyl? If you were WOT on a motor with less than 10 minutes on it that could’ve been a big part of your issue.
Improper installation of parts or improper clearances could’ve been an issue.
Yes a single blown seal can introduce unmetered air into your engine, they put two there for a reason lol.

You need to build this motor properly from the bottom up in a clean environment and do a proper leak down test first and foremost. Then you need to break it in properly and watch your temps and read your plugs until you’re confident in your tuning. It’s pretty hard to melt a rear cyl with semi close jetting if you aren’t going nuts wide open across the lake.
Do some research, it’s impossible for me or anyone to give you a dead nuts jetting spec
and you’ll have to account for your conditions too when basing your jetting off someone else’s similar build.

 

[Radical Riche]

Tore engine down due to me messing with the carbs in the Fall because it was running rich and had a lean run away. That engine was 8 years old and had cross hatch markes still in cylinder s when I took out engine to install a torrent 155 with Carter b tunnel. Anyhow after the run away I decided to put a 1200 jug on it. Well the mechanic accidently put the rear seals in with the 4 tabs on the inside and it blew out. When I first started engine it went wot and I thought something was wrong. I put it in the river, was tuning the carbs and couldn't get a good color on plugs. Thought I needed to up jets. Ordered new jets and discovered rearseal was out. I changed jetting from my 1100 for the 1200 engine to 110 pilot, 135 main, 25lbs pop off/95 gram spring. I had 150 psi compression before I tore it down. I had fresh bore on cylinder, new piston etc. I blame the seals being installed incorrectly. All 3 cylinders have the same amount of slight scuffag. I'm getting cylinders honed, new piston and rings. Also having head checked. When I tore the head off I noticed a rust ring at the top of all 3 cylinders where rings don't ride. I don't like the 1200 head gasket or manifold gaskets. I was told to put them on dry but pro tec said to use a light coat of permatex red spray. I added a 3/8 cooling line and added the water out fitting behind middle cylinder to help keep it cool. I heard 1200 run hot. I see what machinist

Does anyone sell block off plates for 1200?