1991 XV750 low compression pressure on both cylinders (California) (Work in Progress/Completed)

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covenant4935
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Re: 1991 XV750 low compression pressure on both cylinders (California) (Work in Progress/Completed)

Post by covenant4935 » Thu Apr 29, 2021 1:17 am

Update on the running:

It runs but seems the take-off from stationary(1st gear) is kind of lack of power, you have to rev motor up to near 3000 rpm to feel the power to get started. once it's running, shift up to 2nd or 3rd seems OK, power feels right.

Another issue is: when idling after warms up, if i rev the motor up to 3000 rpm or high, it will stay at that rpm and not drop down to the idling 1000 rpm, i'm pretty sure the throttle cables are not stuck, and throttle valves(both of the 2 carburetors) are at the shut position when this "self throttling" happens. Any idea about the cause of this issue? could ti be related to the coasting enrichener system?

Thanks for all the help ;)

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ViragoJoe
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What Virago you Own: 1996 Virago Special XV1100SH

Re: 1991 XV750 low compression pressure on both cylinders (California) (Work in Progress/Completed)

Post by ViragoJoe » Thu Apr 29, 2021 2:49 pm

covenant4935 wrote:
Thu Apr 29, 2021 1:17 am
Update on the running:

It runs but seems the take-off from stationary(1st gear) is kind of lack of power, you have to rev motor up to near 3000 rpm to feel the power to get started. once it's running, shift up to 2nd or 3rd seems OK, power feels right.

Another issue is: when idling after warms up, if i rev the motor up to 3000 rpm or high, it will stay at that rpm and not drop down to the idling 1000 rpm, i'm pretty sure the throttle cables are not stuck, and throttle valves(both of the 2 carburetors) are at the shut position when this "self throttling" happens. Any idea about the cause of this issue? could ti be related to the coasting enrichener system?

Thanks for all the help ;)
There are way too much going on with this bike to really pin point the running issue. The poor compression ratio may be the culprit for lack of power. I have no idea what has been done to these carburetors. Float settings etc., Pilot jetting and main jetting. Diaphragm condition. If there are any vacuum leaks in the hoses. All these things can contribute to poor running.

Look at trouble shooting in your repair manual for poor running.

Sorry, that I can't be more helpful. Just too many unknowns here.
ViragoJoe 🇺🇸
1996 XV1100SH Virago Special
"Never ride faster than your Guardian Angel can fly!!"
;)


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covenant4935
Posts: 47
Joined: Thu Mar 04, 2021 10:43 pm
Location:
What Virago you Own:

Re: 1991 XV750 low compression pressure on both cylinders (California) (Work in Progress/Completed)

Post by covenant4935 » Thu Apr 29, 2021 11:53 pm

It turns out that the problem is the vaccum leak through the rubber boots between the intake and carburetor ;)

New parts are on the way, wait and see :P

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