revtothelimit - motorbike forum

11:1 isn't massively high, but it could be the shape of the combustion chambers, either bigger mains or retarding the timing will stop it pinking

Are the needles adjustable? Raise them a clip if they are, or shim them with a small washer. I'd do that before changing MJs. Oh and are you a hundred percent on float heights?

11:1 is a lot for a Triumph 650 though. Stock is 9 and low is 7.4. Modern engines are up at 13 or more for sure, but they've got much better combustion chamber design. And knock sensors!

I'm pretty sure on teh float height. I also had the needles up a notch (richer) but that made it too rich at low throttle and sooted the plugs up. However, it does have a one size larger needle jet, so if I went back down to stock jet and lifted the needle up again it'd come onto the tapered portion earlier and richen the mix in the 1/4-3/4 range. At the risk of being too lean below that.

But then again maybe I can do that, then add a richer throttle slide. It's already on a richer than stock slide though.

Fucking carbs!

I've always got the main jet correct for flat out running and then sorted everything else backwards from there because the only adjustment at flat out is the main jet, everything else can be adjusted, also it isn't going to hole pistons on part throttle.

Aye that was my thinking too

Le_Fromage_Grande wrote: Wed May 18, 2022 1:45 pm 11:1 isn't massively high, but it could be the shape of the combustion chambers, either bigger mains or retarding the timing will stop it pinking

11:1 is high in an old Triumph, yes partly because of the archaic combustion chambers.

260 main jets were too big on my 650, with 28 mm Concentrics. 250 ones work fine.

Just saying: because other people have 190 jets doesn’t mean you should have.

It has 230s at the moment, as far as I can work out 220 is stock for this bike.

I've just looked, 250s are out of stock on the official Amal shop!

Allens will sell you some VM's that'll fit rather than the Amals

I've started with the valve clearances etc. Doing the clearances is simultaneously really simple and annoying as fuck.

Before doing the valve clearances I went round and confirmed all the headbolts were torqued still....which they are. The rocker box bolts on the other hand were pretty loose, as were the rocker oil feed connection lines. That may explain my excess external lubrication.

You adjust the clearances undoing that locknut then twizzling the adjusters in/out. You can measure the actual clearance using a dial gauge like in that pic, but I don't have one of those so I'm using good old fashioned feelers.

TBH I'm not convinced I've got the feel of feeler gauges . I so rarely have cause to use them!



Like I said it's simultaneously easy and hard. The hard bit is tightening the lock nuts without moving the adjuster. I suspect everyone with one of these bikes has the same two little spanners/wrenches which they always use and which fit just right!

Anyway...valve clearances are OK. I've also got the next two larger sizes of main jet. Switching them over is the next job, along with cleaning all the leaked oil off the engine. Then off we go again.

I found that there's a bit of a knack (with similar bikes). Whenever I tightened things up the gap would reduce and, if I was consistent in the tightening, it would reduce by a reasonably fixed amount so I'd set them too big by that then tighten things up. Worked about 90% of the time. (I was doing them pretty frequently though, which helps).

There's - unsurprisingly - a huge number of opinions on the correct method with these bikes along with the actual clearances to set.

I might go back and do it with the "visual" method, which is to tighten them down until just touching, then loosen off by a set fraction of a turn. The idea is the adjusters have a constant thread pitch and therefore a fixed relationship between turns and movement.

Or i might not.

This bike takes the piss...

I swapped the main jets over last night, I've gone two sizes up. The "takes the piss" part comes from the fact that one of the main jet holders had vibrated loose . How the hell are you supposed to set anything up when all the bolts insist on undoing themselves?

Mr. Dazzle wrote: Wed Jun 01, 2022 7:43 am
How the hell are you supposed to set anything up when all the bolts insist on undoing themselves?

Welcome to the world of old British bikes!

Simple, take it all to bits, balance and blueprint every component... then engineer and fit a balancer shaft.

Easy for a man of your means.

Main jets seem to have helped....I actually chickened out of holding at 3/4 throttle because its too fast. Doesn't exactly feel planted at steady 90mph.

Twas all going great until I broke down. Got not electrics ar all. Currently awaiting RAC.

Yes I did check the (singular) fuse.

Ha ha. Character building

Mr. Dazzle wrote: Thu Jun 02, 2022 9:13 pm Main jets seem to have helped....I actually chickened out of holding at 3/4 throttle because its too fast. Doesn't exactly feel planted at steady 90mph.

Twas all going great until I broke down. Got not electrics ar all. Currently awaiting RAC.

Yes I did check the (singular) fuse.

Oof! Probably find it's been running on an uncharging battery?

On the plus side it's not like the olden times when a flakey English bike was a chap's sole transport.

Yeah I reckon its not charging. I did originally check it was charging but I'll lay odds its just shaken some aspect of the charging system loose.

Started struggling to rev and then progressively got worse before dying completely. I'm like 2 miles from home but it's all dual carriageway.

I used to race a two stroke with a total loss Boyer system, as the battery discharged the max revs dropped. So I think you're right, the battery voltage will have dropped below the minimum running threshold.

Should carry a spare battery