1st gen poor power during acceleration

Hi, i have an annoying problem that is driving me nuts?
I ride an original 1986 vfr 750 fg, it ran fine for years apart from replacing the reg/rect (common problem) but ive recently put the bike back on the road after restoring it over the past 5 years.
The bike revs and pulls fine will a slight twist of throttle but when i twist for more power, it reaches around 6.500 to 7.000 revs then dies of death, sputtering and trying to go but to no avail.
If i change gear keep the revs down its ok.
HELP.
Ive had the carbs off cleaned and balanced them, set the valve timing and checked the basics eg wiring
pictures of the bike can be found on the 1st gen pictures under my username.
Any ideas with a clear head would be appreciated, thanks in advance.
Stevie.:noidea:

 

I would inspect the slides first, make sure the diaphrams are not damaged and they are not sticking. Does it have stock jetting?

 

At 6500-7000 revs it should be on the main jet circuit. does this happen only under load? Or does it do the same thing in nuetral?

 

Hi,
same bike. Check fuel pump/pump relay, if engine dies maybe pump/pump relay does not supply enough gasoline to carbs as you twist for more power.
Then, if carbs are ok, also pulse generators can have shortcut behaviour when more power is requested. Hope this can help !
Ciao and Lamps !
Carmine

 

Hi, thanks for the info, the carbs are stock jetted and this problem happens even in neutral.
I have just checked the fuel pump, but nothing much to tinker with as a sealed unit, the points and spring with connections are fine. `i took a reading with the ohm meter for checking pulse generators and found they were reading a bit high 530 ohm's and 560 ohms according to the clymer manual, the test involves checking 4 out of 6 wires in the multi plug.
The camshaft pulse signal is within readings,
The carb sliders dont appear to be sticking as they all dance at the same time when throttled, but worth a strip down, thanks. will keep all you guys posted

 

Good luck,
try to send a request for help to squirrelman. He is one of the best specialist of 1st gen. VFR.;
some years ago he saved my VFR (electrical troubles).
Ciao.

 

This issue is most likely fuel or electrical. your carbs have debris in them (main circuits). Any rust in the tank/ When's the last time the fuel filter was changed? Will the bike start right up after it dies or does it need a few minutes?

 

I'm gonna put my money on the slides and the needle Jet that's inside them.

I had a similar issue with my 2nd Gen

 

How to troubleshoot this problem...

We need to determine if the problem is related to a particular rpm range or to a particular throttle position. Put a piece of tape around the throttle grip and mark some reference points for closed, wide open, 1/2, 1/4, 3/4, 1/8. Now run the engine and observe if it cuts out at a certain throttle position as you raise the revs, or if it cuts out at a certain rpm regardless of throttle. If it truly is rpm-related then it is likely an electrical issue.

 

I had a similar issue with mine last year. 85 Vf700. Pulled hard at first then seemed to die off... sputtered...I bumped up the jet sizes and that cured it.

Sent from my X500 using Tapatalk

 

I'm thinking it's running out of fuel due to an old fuel filter that needs to be replaced. honda recommends every 10000mi on these.

 

Have you inspected/changed your sparkplugs anytime in the last few years??

It's usually best--if you don't have alot of experience reading sparkplugs-- to simply replace them and eliminate them as a possible problem. Deposits coating the ceramic insulators can interfere with sparks at high-rpm, open throttle conditions.

If that don't fix 'er, you'll need to check fuel pump for output volume and slide diaphrams (as Toe mentioned) for punctures or tears, and that can't usually be checked reliabily just by watching slides rise while the bike is at rest but need to be inspected visually.

 

Hi guys a short update, i purchased a new reg/rectifier, fuel filter, had the tank drained and cleaned with a compressor.
Took all the coils off and stripped the HT leads down by unscrewing the brass cap where the plug sits, there is a spring and a fuse shaped insert that was corroded, this contacts with the HT lead itself, ive taken pictures and will upload them when i get time.
But to no avail, it still sputters, sounds like a dragster when misfiring, so im going to remove the carbs again to check for faults.
Thanks.

 

Always a good idea to remove the sparkplugs for inspection BEFORE digging into the carbs cuz the plugs may tell you where to look first.

Could be a problem with not enough fuel getting into carbs or electrical or........

 

Hi, thanks for all the ideas to keep me interested, im sure i have overlooked something simple. I have checked the plugs a few times, even put the old plugs back in just in case there is a fault with them, there is a slight discrepancy with number 2 plug so thats where im going to dig further.

I changed all the coils to eliminate that but no difference, have been thinking that if a valve has a weak or broken spring it could show this kind of symptom at high revs, but without removing the head it's hard to establish, with 2 springs in each valve, or am i diving to deep for answers.

Any feedback with this would be greatly appreciated, thanks.