Harris G80

[OEW591]

A friend has an early Harris G80 he cannot get to idle properly, the engine will stop unless the revs are built up slowly and once on the road the bike is fine, pulling an indicated 80mph.
He has the original airbox and a massive Dell O'rto carb - later bikes have a smaller carb and can fit a pancake type filter.
Is there anyone in cyberland who has any experience of these bikes that could offer a few pointers as to what to try, spares etc.
Unfortunately he doesn't have web access and the poor chap is just about at the end of his tether.

[paul knapp]

Alan,If the carb is "massive" this could be the problem as the air speed through the venturi would not be enough to pull a steady metered flow of fuel in to the engine at low to mid range, if the throttle were to be opened all but slowly. There would be an unbalanced fuel to air ratio causing the engine to have a massive flat spot, big bore carburettors are good for top end revs but inhibit the lower end of the engines performance. Maybe this is why later machines have a smaller carby? Has the bike been used for competition? The cams and compression may have been altered and / or it may have been jetted for alcohol fuel which would adversely effect idle (although I am sure you would see the excess black fuel smoke if that were the case) and low revs performance, gosh, what a tin of worms have I opened up.It may be only that the idle/low speed jets just need a simple clean out. See what the experts? have to say.
Cheers PAUL
Down under.

[gleng80]

The Harris G80 is known for starting and slow running problems.There are a number of things to try.
First the carb should be: 36mm Dell Orto PHF 36 B5 Choke dia:36mm Slide:50/3 Needle:K4/2 Main jet:120 Pilot jet:58 Starter jet:65 Accelerator jet:35. There is a rubber diaphragm which can become split and cause problems. The drain plug should be cleaned out at 3000 mile intervals and the float height should be checked.

The plastic airbox quite often becomes split. This should be carefully checked. Next check the rubber connections between the carb/engine and carb/airbox, these can perish and allow air in.

Check the valve clearances are spot on (.05mm) and the HT lead and plug cap is OK (worth changing). Fitting Platinum or Iridium plugs have solved some Rotax problems.

Does the bike still have the original silencer?

As a last resort, changing to a 34mm Mikuni carb has also been known to solve slow running problems.

[OEW591]

Thanks Chaps

The airbox had collapsed at the back so He has repaired it with an aluminium plate and fibreglass. He has also found that a K&N filter from a Commando will fit carb mouth and the bike runs OK.