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Discussion Starter · #1 ·
First......Great Forum!...came across it while looking for answers....glad I found it.

I came across an 1987 SRV 540. I messed around and got it running pretty good. I got one problem.....

It starts easy....Idles fine. When you punch it (WOT) it runs excellent (7k RPM)for a couple seconds then falls to 5000 rpms or so and wont go any faster. If I stop for a couple seconds then hit it it does the exact same thing.

Is this a fuel issue? Is the float bowl running out of gas....pump not keeping up?

ANy body had experience with this I could use your help.

Thanks



P.S.
It has the stock keihin carb.
I have taken apart and cleaned the carb.
No airbox....looks like a K&N filter.
I disabled the oiling system.....I run premix
 

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I found a ripped diaphram in my fuel pump causing my engine to starve at high rpm I have the same motor. If yours is easily accessible remove the lines from it and unbolt it and take the screws out of it remembering exactly how it goes back together and check the screens in it. Some scribe on it with a pick so its easy to match the plates up upon putting it back together. Not a tough job but tedious it its hard to get to.
 

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Sounds like the driven clutch isn't shifting properly causing it to bog. Have you cleaned it recently? Both Drive and driven should be done at the beginning of every season.
 

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Discussion Starter · #4 ·
Thanks for the replies!

I thought the same thing...maybe fuel pump. I put a different pump on and it acted the exact same way...so I dont think thats it.....Unless both pumps are bad. But it runs to good for that I think.

I havn't checked the clutches. When it bogs back to 5k rpm it will back fire if you stay in it.

Is there a way to diagnose the clutch not shifting correctly? I will clean em just in case.

The backfire makes me think its fuel related but I could be barking up the wrong tree.

Thanks
RBBH540
 

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The backfiring changes everything. In regards to the shifting.
Have you replaced the plugs could be fouling. But it sounds like dirty carbs and or bad fuel. Look and see if the inline fuel filter (if you have one ) isn't dirty and partially plugged.
 

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Discussion Starter · #6 ·
That makes sense. Its got to be in the filter or maybe pick up tube. I am gonna try to get to the pickup and filter...see if thats it.

Before I started it I drained some pretty bad stuff out of the tank.

It runs to good otherwise to be anything major....at least thats what im hoping. It must be starving for fuel when its really hauling.
 

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backfires through carb or exhaust? could be a timing issue or corroded flywheel. once you rule out the fuel issue, thats where i would look next.

if you ran bad gas back into your clean carb, you may have to clean again.
 

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Discussion Starter · #8 ·
Well...I put a new pickup tube and filter in the tank......same thing still happens. Put a different coil on it. No difference. I am stuck on this one.

It will sing....runs perfect for a couple seconds at wot....then bogs to 4500/5000 RPM. Even if I stay in it it will only max out at 5K until I slow way down. Then its back to running good for a couple seconds.

Is there an electrical problem maybe?

Please keep posting ideas...I will keep trying everything thrown at me.

It doesnt seem like anything major because of how easy it starts and runs.


Thanks
RBBH540
 

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since you didnt mention the backfire again, its starting to sound like clutching. overshifting and loading the motor too much until the secondary backshifts as well as the primary regaining control of the shift.

i know these sleds were very finicky with timing. i had 2 from that era, working on one right now. if the timing was off by even the slightest amount, power losses under full load would arise.
 

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Discussion Starter · #10 ·
Sorry...thought i edited post.

It does backfire occasionally right after it throttles down to 5k. exhaust backfire...not everytime, but at least half. I will check the clutches.
 

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pay attention to the belt positioning in the secondary as well as any scrub marks from the belt on the primary. just some telltale signs.

lets hope its not ignition related.
 

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Discussion Starter · #12 ·
Thanks for the advice!...I will check it out this afternoon. I have a identicle parts sled....Im thinking of switching the cdi box just to see.
 

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Discussion Starter · #13 ·
f I read right these engines have reed valves on em.

What do they do and could they cause the problem Im having?
 

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yes, your sled has reeds and it could be a factor.

remove the carb, remove the intake manifold, and the reed cages are located between the manifold and the cylinder.

look for any chips, warpage, or abnormal sealing of the pedals to the cages.
 
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