Carb issue or pulse generators?

Hi chaps - a brief refresher regarding my bike’s history. I bought her with 70 miles on the clock after she had been sat for nearly 20 years in the former owners living room.

I have had what feels like fuelling issues from day one. The bike was never laid up and the tank remained half full. My mate stripped the carbs and cleaned out the visible gunk and the jets that were removeable. He didn’t touch the air mixture screws and was only able to clean the choke jets in place. With the bike put back together she’s still not quite right. You need choke for a long time before you try to pull away or she dies. I’ve been running her in so no excursions above 5000rpm which has meant performance above this point has not been evaluated. Today, after the first service I took her to 6k and she started to hesitate quite badly.

I have heard that pulse generators can cause similar symptoms but I may be putting 2 and 2 together and making 5…

Another thing we have noticed is just above tickover the carb sliders are chattering a lot.

At the moment the main issue is that at tickover if I blip the throttle the bike dies. If I lift the revs up to about 1500rpm (which seems to correspond with the chattering stopping) then blip the throttle, then it revs fine.

I’m thinking of getting some seafoam as it’s now available here in the UK via ebay and wondered if any guys on here have used it. Failing that would anyone have any further thoughts please?

That sounds like a find and a half! still not even run in after all this time!

My bet would be on the carbies still being blocked.

If the pilot circuit is blocked ( mixture screw is part of this) then it won’t idle properly, this and the slow jet supply fuel during initial move off and lower end of the rev scale,so by having the choke on it is compensating for the lack of fuel but will still be a bit ‘gutless’ and run pretty poorly.

Also check that the diaphragms attached to the slides are not perished or have holes or cracks, if they do then you will be lacking power as you wind her up as they won’t be working properly. It’s also possible that some of the internal pathways have blocked up and are causing problems.

Ideally the bodies and all jets should be cleaned in an ultrasonic cleaner as this can remove all buildups from the internals of the carb bodies and jets.

These guys can do the carbies and replace the diaphragms if needed.

and here is some info on rebuilding V4 carbs

Good Luck!

Thanx for that Planty, yes she was quite a find. I’m up to 800 miles now hehe!

I spoke with NRP regarding the chatter of the slides. Of course it’s hard to tell what’s “expected” and what’s excessive, particularly as the filter being removed will have a small effect on it too and you can’t see if they chatter with the filter in place. They suggested checking the plugs to see which cyl was causing the problem. All plugs seeemed the same. Cleaned and no change. They mentioned the diaphrams but they all checked out ok. All sliders seem to fall at a similar rate too. I think you’ve got it with the blocked jet. I have seafoam on order now and hope it will arrive with me in about a week or so. I’ll use that and try to leave it in the carb bowls for a few days and see what happens. I shall update after that.

Thanx again - Ian

Another method of clearing out aged crud from innaccessible carb passages is an ultrasonic bath. It’s non aggressive and gives good results. A lot of restorers now prefer that method over traditional ways, like seafoam etc. Worth bearing in mind.

Thanx scratcher. The carbs have been off once though and I’m disinclined to have them out before trying this. They’re a bit of a beggar aren’t they…?

Courageous I have fuel blockage symptoms on my FF (laid up for 7 years fuelled before I saved it) The carbs have been removed and cleaned but still a bit rough and will not rev over 6k. I have ordered some Profi Fuel Max which is added to a tank of fuel and supposed to be excellent. I will update this when it arrives and I have tested it. For a tenner thought it must be worth a go…

Skullster - thanx. I’d appreciate that. Sounds a little similar eh? Cheers - Ian

Hi Found this good description of how to clean out carbs:

and another here:

I just got my second vf1000…I foud this one with 22,000 miles on it and the vin is number 424. =)
The first one I owned was 18 years ago and drove it cross the US.
I got this one at the end of April and it now has just under 32,000…but she is also. Cutting out at high rpm…but not all the time…most of the time…but everyonce in awhile I get that kick in the pants at 8k when normaly it just sputter and cuts out…it acts just like a rev-limiter.
I have taken the carbs off and cleaned them…it stared to idle st 3600 because the other owners just bumped it up when it was gettting cloged.

Was anyone able to fix their problem?


Hi Pummel In the end i got my carbs cleaned in a ultrasonic bath. I also found the fuel tap and filter gunked up with rust and crud from the tank. Cleaned it all out and she revved up and scared the pants off me ;-)This winter I’m going to clean and sea;l the tank to sort it properly.