Lack of top end power and pinking

Been stretching the v35’s legs more and it seems to run out of steam a bit early and pink in 4th at 6-7000 rpm when hot

If I back the throttle a shade i get a little bit more go

Getting some intermittent pinking when hot and pulling hard up hills

Any tips on where to start ( carbs clean and balanced , factory electronic ignition and standard air box )

Plugs new , slightly sooty but only done 275 miles in 30 years

Start with little or no choke

Pre detonation (pinking) can be cause by the build up of heated carbon deposits in the combustion chamber but also the incorrect grade of spark plug.

If it’s starting from cold with little or no choke that might suggest the initial carb settings are too rich.

I don’t know what the compression ratio is but I’m assuming your engine runs happily on unleaded? I know that some bike engines from the '70’s would only run properly on 5 star leaded fuels.

Also worth rechecking would be the ignition timing, particularly that the auto advance/retard setting is correct.

Good luck anyway.

Sounds exactly like what I had on my 850 back in 1990, previously had put ‘new’ VHB 30 carbs and K&N filters on, turned out main jets were still slightly too small. Only most noticeable when hot and especially in hot weather.

You may have correct size main jets but maybe find they have been slightly constricted by the hard deposit left behind by modern unleaded when it’s left to dry out in the float chamber.


had carbs apart and notice 4 rubber seals are missing, one from each of the choke top mount plates and from the 2 jets that push in to the corner of the float chamber

no chance of getting parts today but have cleaned and re assembled carbs

carbs were fairly clean with minor trace of something where needles have been sat for years

get mixture to 1 1/4 turns from seated and its pulling much better down low and still takes of like a 2 stroke at 3500 rpm .

doubt timing can be out as it originally fixed electronic pickups behind the alternator

main jets are 102’s which matches up with the original spec

oddly later v35 mk2 and v35c have 108’s as standard

not sure if to stick some 108’s in and see.

Don’t plan to fit K&N’s as the crank case breather and filter works nicely for once…!

Simple way to check, when it’s doing it does pulling choke on improve it, or make it worse. If it helps, it’s a bit lean, and vicer versa.

As regards cleaning the carbs, I’ve found that the brown / green deposits can be so hard they won’t shift with carb cleaner etc., has to virtually be scraped off, if it’s inside a jet and constricting the hole diameter how can you tell, without a new or clean one to compare it against, as I found out last year. Once you know, it could be CAREFULLY poked through with copper wire to scrape it out v


If all else fails it might be worth checking the rate of flow through the fuel taps. I drove myself crazy chasing a similar fault on an MZ a few years ago. It ran fine util it came to a hill or you gaveit a bit if stick and then it would just die. Turned out the tap was partially blocked and it was emptying the float chamber faster than it could fill.oafski2014-04-12 22:58:26

have you got electronic ignition or points ??had a case a while back where the auto advance unit was sticking

If it picks up a little when you back off the throttle it’s usually a sign of a weak mixture which can be due to many things but most likely restricted or too small main jet. Get the missing seals fitted and if it’s still running the same them pop in some 108s they should only be a few quid. Also, if you can hear pinking at high engine speeds it’s pretty severe so don’t hold it in that position for any longer than you have to. Tesco super unleaded (I think they have a fancy name for it but can’t remember it off hand) comes out of the pumps at close to 100RON so try a drop of that. If it still pinks on that you’re in trouble.

I would just bear in mind that there is a significant amount of adjustment on the pick-ups, it would be possible for the timing to be out. It is worth checking the timing with a strobe if you haven’t already done so, also I think I’ve read that the the air gap between the rotor and the pick-ups affects the amount of advance. As over-advanced ignition can cause pinking I reckon It’s worth a look.

i upped the main jets to v35 mk2Â spec and the top end power has come on a treat and no pinking since, fairly sure it was leaning out.not long moved house so strobe is missing in the clutter but plan to check asapguzzi-v352014-04-27 08:12:54

I hate being right all the time

Check float heights. Check that awful airbox abomination, for gaps / leaks.