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

Radical Riche

Radical Riche

Location
Lower Burrell Pa 15068
DylanS said:
You can take a gasket to any machine shop or guy with a plasma cutter and have one made.

So you had a lean runaway which was almost certainly caused by the rear seal and the cylinder closest to the seal melted down first…. Sounds like you found your issue
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Great idea with the gaskets as a template. No, I had a lean run away when my engine was a 1100 and I was adjusting the carbs due to it was running rich. I fired it up on my jet ski dock and it went wot for a long time, which I can't believe it didn't seize up. Anyhow it never ran right so I tore it down, went with a 1200 jug after modifying my 1100 case. Got new crank ,bore jug, rejetted carbs etc. On the first start up it went wot. I poop it down, fired it up again and did the same. Thought idle was out to far so I cranked it in..looked like butterflies were closed..they probably were cause it was sucking air threw rear seal. So the mechanic put the seal with 4 tabs on the inside. I didn't melt a cylinder, all 3 just scuffed a little. Have head at machine shop to make sure it's not warped. Machinist wants to now what c.c. the stock oem comes are..how could I find that out? Thanks!
 
DylanS

DylanS

Gorilla Smasher
Location
Lebanon Pa
well you see… I was riding in a very specific stance.. one that some people may not particularly agree with… and suddenly a bolt of lighting struck me and when I woke up I was laying (pants down for some reason) on the shore and quickly grabbed my Canon EOS-XD1 camera to snap this high quality image you’re seeing.
Very fortunate to be alive.
Unfortunately both my mikuni DF62 fuel pump and my rear seal were destroyed in this bizarre accident. Really quite tragic but happy to be here today.
 
Radical Riche

Radical Riche

Location
Lower Burrell Pa 15068
That's what I thought. The external fuel pump saved my engine. If I had internal carb pumps than the engine wouldve keep running and smoked crank and major cylinder damage. Very little scuffs, just needs honed, rings and pistons.
 
Radical Riche

Radical Riche

Location
Lower Burrell Pa 15068
Okay, why did the 1200 go with 3 pulse with internal carb pumps and the 1100 went with external fuel pump and no pumps in carbs? That's what I'm wondering why yamaha didn't use external fuel pump on the 1200 but did on the 1100?
 
WFO Speedracer

WFO Speedracer

A lifetime ban is like a lifetime warranty !
Location
Alabama
Ask Yamaha I am just a lowly technician not an engineer. I do know they made lot of changes geared toward making them stay together longer, staggered timing, staggered compression are the two main ones, this may also fit into that picture. I can say without a doubt the 1200's stay together better than the 1100's ever did.
 
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Radical Riche

Radical Riche

Location
Lower Burrell Pa 15068
WFO Speedracer said:
Ask Yamaha I am just a lowly technician not an engineer. I do know they made lot of changes geared toward making them stay together longer, staggered timing, staggered compression are the two main ones, this may also fit into that picture. I can say without a doubt the 1200's stay together better than the 1100's ever did.
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I got over 8 years out of my 1100 till I messed with carbs and had a lean run away. Is that why the 1200 runs that partially restricted exhaust manifold gasket to keep the rear cylinder cooler? I read that about group k and rear cylinder problems. I'm just tore on if I should go back to fuel pumps in carbs with their own pulse line instead of external carb. Brandon that ownes Havasu PWC told me that a external fuel pump on a 1200 wont work that it sends the wrong signal to carbs. This s@cks! Thanks man!
 
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