1991 Yamaha TDM850

Classic Motorcycle Mechanics - - WORKSHOP -

Q:I’m hav­ing trou­ble get­ting my bike to run cor­rectly. It pops and splut­ters, not in the early morn­ings though, mainly at idle (12,000 to 15,000rpm when warm). I have been on the TDM fo­rums, changed the emul­sion tubes, checked nee­dle heights, di­aphragms and fuel fil­ter. I’m chang­ing the ex­haust seals next, but I doubt even that will work. What should I con­sider? The float height is spot on, the choke plunger doesn’t look like it’s leak­ing and I’ve set the idle screws to the man­ual. I’m ready to send it to a garage, but I hate spend­ing money on some­thing that I can do my­self! With a lit­tle help, maybe? Merv Martin

A:The first thing I should say is that your idling speed of 15,000rpm is prob­a­bly a lit­tle too fast. Okay, 1500rpm! But se­ri­ously, even that is a bit too fast as it is meant to be 1100 ± 1000rpm. The symp­toms you de­scribe in­di­cate ei­ther an ig­ni­tion fault or an ex­ces­sively weak mix­ture. You say it is okay early in the morn­ing, and I as­sume you mean when the en­gine is cold and hence the choke is on. First, make sure the ig­ni­tion sys­tem is just as it should be and it might be a good idea to change the spark plugs which should be NGK DPR9EA-9 or DPR9EIX if you splash out on irid­ium-tipped ones. As­sum­ing, as you say, ev­ery­thing within your car­bu­ret­tors is cor­rect in terms of fuel lev­els and jet spec­i­fi­ca­tions, then you should check for sources of air leaks. This in­cludes the mount­ing rub­ber tubes, which should be pli­able and prop­erly clamped and a few O-rings which should be changed as a matter of course, es­pe­cially the two at the joint be­tween the di­aphragm cover and carb body. It is pos­si­ble to fit the cover with the di­aphragm not cor­rectly seated so check this. A few own­ers claim that the jet within which the nee­dle slides, part num­ber 3GM-1414-194, wears and causes prob­lems but I do not think that is the is­sue here.

Newspapers in English

Newspapers from UK

© PressReader. All rights reserved.