Hello everybody. My 850T has been running well for several months but about a week ago as I was nearing home after a ride of about 20 miles, mostly motorway, except for the last few miles the engine began to continue to run fast after I closed the throttle. The symptoms were identical to sticking carburettor slides. The carbs are VHB30’s, newish Venhill nylon cables and light return springs which have been faultless up to now.
After checking and refitting cables, springs and slides no improvement. I’ve rerouted the cables several times with no change and just changed the springs to the original strongest ones but to no avail.
I can find nothing wrong with the throttle cables and carbs. The bike starts okay but when it gets to working temperature the engine begins to race again. What am I missing? Could something else be causing the problem? There’s only so many times I can take it apart to find nothing wrong and then the same problem is still there.
Regards Dave
You have checked the cables but are they getting trapped anywhere? If they are movement of the bars could stretch the cable and raise the revs. Unter the tank I pass the cables throught a short length of fuel pipe each side at pinch points so they don’t get trapped.
Hiya Chris. Yes, I also have lengths of fuel pipe on mine. In desperation at the moment the cables are running loose outside of the petrol tank. Apart from putting back the strong return springs nothing has changed since the fault developed near the end of the last proper journey I did over a week ago. Since then I’ve dismantled the relevant parts, reassembled them and when I stert the engine everything’s okay but on a test run when the engine warms up it’s exatly as if the slides are sticking. Take it apart, put it back together same result. If I had any hair I’d be pulling it out by now.
Guzzis. Character building aren’t they?
Dave, my recently rebuilt Spada has developed the same issue (Spada has same carbs) I’m working on the assumption it may be an air leak. Cables and choke slides are new. Doesn’t feel like sticking throttles. Ive read that spraying some WD40 around the carbs is telling but I dont want to set fire to three years work so I wont be doing this. Subject to the weather I will be doing more work on it this week. I’ll let you know how I get on.
Andrew
Thanks for that Andrew. Mine has been running well for three or four months. The only thing I’d done before that was to check the valve clearances which were okay anyway. This present fault developed from nothing. I’ve not touched the carburettors and I’ve checked and rechecked carbs and cables several times. I’m confident that the slides are dropping but how can the engine be running at above 3000 rpm when the slides are down. Ive not checked for air leaks so perhaps that should be the next step.
Regards. Dave
I had something similar a long time ago and it turned out the carbs were well out of balance.
You say cables so I assume you have a twin pull twistgrip and one cable to each carb. A very easy check is to close the throttle and listen for the clicks as the slides hit the bottom of the carb. They should drop together at the same time, if they are out of balance, one will click before the other.
Don’t set the tickover by adjusting the cable adjusters, use the screw in the side of the carb. When the throttle is released, there should be a bit of slack in the cables.
Another possibility is that the outer cable is getting hooked up on the edge of the adjustor on top of the carbs.
Don that is a good call, if there is too much slack in the cable
This might be totally irrelevant, but here goes anyway… is it worth a look at the Plug colour//Choke jets; on my V50 the plunger seals were well worn and not sealing… result very rich running, not helped by an over tight cable…
Thank you all for your sensible suggestions. The slides are both landing together. Neither of the cables are being held up at either end.(I had that once before). Both plugs look okay. Can’t detect any air leaks but I’m going to put new insulation spacers between the inlet tracts and the carburettors and new gaskets where the top of the carburettor screws down. If nothing else, that will eliminate any air leaks that may be there.
I hope then that the problem is eliminated. If not, I’ll start at the beginning again.
I wish I lived closer to Nigel Billingsley of N.B.S.
But I don’t. Watch this space!
I use Tony Botto at Didcot
he knows his stuff, and does racing bikes, and also has a nice restored Guzzi
might be worth sending it to him if you are not far away
ps have you by any chance used that horrible E10 fuel ?
it made my machine run like a cement mixer
Nowhere near Didcot. I’m in sunny Bolton. No I steer clear of E10 fuel. I’m collecting the insulating washers from Gutsibits tomorrow so I’ll replace the old ones and that should eliminate any possible air leaks. Regards. Dave
I envy you having Gutsibits on your doorstep. The only thing I’ve found with my Spada was the left hand throttle cable has virtually no play and adjuster is fully in. Doesnt seem a problem while idling but when warmed up on the road rpm is slow to return from 3k. Maybe its as Don says and it throws the balance. Anyway going to reterminate the cable or make a new one up.
Andrew
That sounds very similar to the fault on mine Andrew. I usuallyhave items posted from Gutsibits, it’s an 80 mile round trip but on this occasion I want the parts asap. The earliest I can go is this afternoon. Other things in life getting in the way! I can’t see any air leaks but I want to eliminate the possibility so that I can concentrate on slides, cables etc. I’m going round in a circle and achieving nothing.
I’ll just add that Gutsibits are very prompt at posting but I thought I could get over there first thing, however as I said, other distractions in life!
Regards. Dave
Just a thought, you have got the slides in the rightway round? The larger flat face goes to the engine.
Make sure the cables are seated correctly in the slides and the twistgrip Is it 2 cables all the way or does it have a splitter under the tank?
Thanks Don. The bike has been running well for a few months. Near the end of a fastish ride a couple of weeks ago as I arrived home the tickover had become too fast. I put the bike away and next time I started it as it warmed up the tickover increased without my touching the twistgrip until it was showing above 3000rpm on the tacho. Since then Ive had the slides, cables etc. on and off several times with no change. Everything obvious looks right. i.e. slides the right way round the etc. I’m now trying to find any potential air leaks because if the slides are both seated (which I think they are) how can the engine revs increase? Watch this space!
Have you checked the chokes, mine was like this and was choke on one side?
Thank you for your suggestion. I hadn’t thought about the chokes but I will check them as soon as possible. Maybe later today. Regards. Dave.
the choke pistons can stick, through corrosion build-up - also, they have a ‘rubber’ pad at the end which can become indented after time, affecting seal (presumably).
Unfortunately the bike has to take a back seat today but I’ll be checking the chokes when I get to it. I now have new insulation spacers for between the carb and the engine to eliminate any possible air leaks from there. I feel the solution is staring me in the face but I’m missing it so I’m trying to check everything that could be causing the issue. Regards. Dave.
Definitely worth replacing old inlet rubbers for new. You can’t go wrong even if that’s not the problem.
R