Custom/Hybrid General Tuning Question

[Tmart]

Hey guys, I've recently acquired a ported big bore motor that will be here in a week or so and it was run on 44's but not the 44's (Oem) that are coming with it. I haven't really ever tuned anything on my past ski so I didn't know if I could send the motor and carbs to a company and get it tuned right? That way I'm not playing the guessing game all winter and into next summer. Thanks in advance for replies

 

[McDog]

Ask the motor builder for jetting specs and we can dial it in from there. Who built it?

 

[Tmart]

Thats the thing, he doesn't know the specs and the exact history on the motor b/c he bought it from somebody. KTM434 ran it on full spectrum 44's and i'm gonna be running them on OEM 44's

 

[McDog]

Well that sucks. Find out specs for other ported big bores and we will have to start there. It will take some tinkering and eat up a few rides to get it right. You will get really good at removing those carbs.

 

[Tmart]

Well that sucks. Find out specs for other ported big bores and we will have to start there. It will take some tinkering and eat up a few rides to get it right. You will get really good at removing those carbs.

Haha don't tell me that. I've heard that these OEM carbs aren't gonna be enough for this motor. Got anything on that?

 

[Buckwild12]

Depends, Jetmaniac big bores are setup to run on 38's you may be ok

 

[Nuklear6]

How big of a big bore? How much compression? What ignition? All this matters when speaking of carbs required for the engine combination. But as said above 781 running on 38s with great results. And I think oem 44s are sufficient enough for up to mid 800cc engines if tuned properly. Only asterisk is I think total loss and high compression can demand more carb potential ....

 

[Tmart]

The bore is 780, running and will be running on OEM 44's with stock ignition. The compression is 180 on both

 

[Pablo]

Decent reference here, not a bible on the topic, but atleast a starting point.

http://www.x-h2o.com/threads/19403-...-SuperJet-and-Blaster-1&p=1200643#post1200643

 

[McDog]

The carbs will be fine even with more compression and a total loss ignition.

The thing to know here is that tuning carbs for unknown porting can be a nightmare and eat up a lot of potential ride time. We don't have a pro jetting kit with every size at our fingertips so it will be trial and error with waiting time to order new jets between rides. This is why sometimes the best priced engine isn't always the best deal. Pay upfront or pay later with aggravation and lost ride time. Paying more for a complete tuned setup or for an engine ported by a reputable builder is worth it imo.

 

[Mark44]

This thread and a proper tach will get you set, no need to guess.

http://www.x-h2o.com/threads/39846-Tuning-tips-for-Rookies.

Watcon has the PET tach.

 

[Tmart]

Thanks Mark. In the thread Pabloescobar posted I found a package thats pretty much my exact package. I know its probably not gonna be perfect, but hopefully with a tach and that starting point, hopefully I can get it

 

[Waternut]

Since you found an engine that's built similar to yours, order 2 jet sizes above and below what worked for that guys setup. It's not rocket science but it takes a little getting used to in order to understand the sounds and symptoms of lean or rich tuning. More power to all those who tune with tachs... I can't tune an engine with a tach to save my life.

 

[Tmart]

Since you found an engine that's built similar to yours, order 2 jet sizes above and below what worked for that guys setup. It's not rocket science but it takes a little getting used to in order to understand the sounds and symptoms of lean or rich tuning. More power to all those who tune with tachs... I can't tune an engine with a tach to save my life.

i have an idea...i'll spend all day at the lake one weekend and you guys can help me tune it! :shocked:

 

[Matt_E]

As an added bonus, by the end of it all you'll understand why people love intake manifolds with separate carb plates.

 

[WFO Speedracer]

Or you can send it to me , I will mount it up in a Blaster and tune it in for only $1000.00 lol

 

[kevbo]

Since you found an engine that's built similar to yours, order 2 jet sizes above and below what worked for that guys setup. It's not rocket science but it takes a little getting used to in order to understand the sounds and symptoms of lean or rich tuning. More power to all those who tune with tachs... I can't tune an engine with a tach to save my life.

Small carbs tune great with tachs. By the time I get best response with a 44 or larger the top screw is always rich of peak rpm. Make it sputter at 1/4 throttle with the pilot and turn the top screw until it pulls hardest.

 

[Blue]

We use the 38s on our bigbores, contact jetmaniac we have all the specs for jetting right down to how many turns on the needles to make it rip. Thats if the portings correct. Besides the 38s will hit harder than OEM 44s and use half the fuel.

 

[Tmart]

We use the 38s on our bigbores, contact jetmaniac we have all the specs for jetting right down to how many turns on the needles to make it rip. Thats if the portings correct. Besides the 38s will hit harder than OEM 44s and use half the fuel.

Thanks Blue, thats the response I was looking for.

 

[McDog]

So your ditching the 44's for some 38's?