SRV Mod

K

KCCats

Member
Joined
Dec 18, 2006
Messages
49
Age
65
Location
IL
I have built this sled for the past 10 years or so
Got jetting info from SLEDNUTS and it ran OK for many years
Went to clean the 40mm carb this preseason and found why it only ran about half throttle
The slide just barley opened 3/4 of the way!
So I put a 38 bored to 39.5 and basic same jetting and it was better but had to have the choke on!
Long story shortened, No air leaks and barely runs on choke!
It will sit and idle all day!
Carb cleaned re jetted, same!
Sprayed the boot and seals same!
What am I missing?
Next step is to pull engine and check seal behind flywheel?
 
Yes
I have now tried to go down to a 38 that came off my 88 650 WC that are bored to 39.5
Same
Tried the big 44mm with the dyno jet same!
I went and removed the fuel tank and strapped a gallon tank to the bars and gravity feed the pump
(doing away with the pick up filter in stock tank)
It acts like it is running out of fuel
Changing float heights, main jets, needles, jet needles, complete carbs, nothing has changed!

It will run GREAT for about 50', skis in the air, then fall on its face!
 
Replace the pulse line. It maybe leaking and loosing vacuum? Or cracked.

Also try a fuel pump off another sled or buy new. Keep us posted. Good Luck.
 
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Yep did that
Tried a mikuni round dual outlet with one outlet capped off!
Then added the small tank to bypass the pick up in the stock tank.
 
So i don't really understand the symptoms.

Idles but won't rev up under throttle?
 
It will idle yes
It will Launch!
It will pull really strong for about 50 feet!
Last run I did, had the fuel tank off the sled, small 1 gallon fuel cell strapped to the bars.
Idled out to the bean field 500 feet away ran good
Lined it up and nailed it!
Had all I could do to stay on the machine (seat loose) and then broke the windshield with my Face!
All that in 3 seconds!

Could something like my stator plate be loose?

I have had the motor completely torn down and rebuilt, only has about 750 miles on it!
 
Yikes. Sounds dangerous.

Loose stator? No it would not run timing would be way out. Could be a bad CDI Or coil. Spark cutting out under load.

Could also be a bad reed valve. If you are running metal reed stops? Check the reed stop for cracks. If a reed stopper cracks...it throws the reed out of time with the engine. It will fall on its face instantly. Was a real problem on the red head triples. Cracked reed stoppers.
 
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Reeds are Boysen two stage.
Tried with out reeds stops, with reed stops, flip the reeds, Nothing
 
Dang it. If crank seals are not leaking and no intake leaks. It must be an electrical issue.

One other thing. Do you have stock Reed's to try? I had an issue with my Boysen Reed's and 44 VM carb. Alot like your. Start and idle perfect. Fall on it face under full throttle. I chased fuel and carb tuning around for two days. Finally swapped out Reed's for stock reed. Sled run perfect. Does not miss a beat. Just a thought.
 
have you tried adding a ground from the engine plate to the chassis? had to do it on older sleds before for issues while they where running.
 
Just a source coil and trigger coil as far as i know. If the source coil is weak? it will act up and lay down under full throttle. Experienced this once in a high mile Phazer.
 
HMM
My TCat had a weak stator and would only have enough power for two of the three cylinders.

This sled came with a Mikuni round single outlet pump, that I have rebuilt.
What is the output?
I have a good double out with one capped off, but the inlet and outlet are smaller (8mm v 6mm)
 
This is the early fuel pump later years mid 80 maybe they changed the pump up.

Funny thing. I rebuilt this pump with a jobber kit. It has never worked right since. I had a spare brand new single pump. Installed it and sled runs fine again.
 

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Can't say I've ever seen one like that?
Mine came with the Mikuini round single with 8 mm in and out
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1990 Yamaha SRV (SR540P) Air Cleaner

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Fuel Pump Assembly (8Y0-24410-0

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Thats insame!
 
Update
Pulled the stator and have at least 1 burnt coil!
Shipped it off to Blaine
 
Had this happen with my SRV drag racer years ago. Turned out that I had over torqued the spring in the secondary. It would launch perfect at 5000 pulling skis off the ice and then the secondary would go from closed to full open and almost throw me over the handle bars. When I let off and hit it again it would do the same thing over again.
 
I figured I had multiple issues, I did!
Too lean
Too rich
too much oil
I pulled it apart and I pitted the piston tops and heads real bad
Took out the ring on one exhaust
 
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