throttle body balancing (again)

[jonogs]

Help

Being a semi-competant mechanic I decided to have a go at a balancing the TBs as per the advice given in Rob Lentini document I got off the web a few years back.

So far I have built my own manometer (4m of tubing half filled with light oil - watch those exhausts though!!!) and adjusted the throttle stop screws so that I have a fine idle balance. (With brass bypass screws at 2.25 turns from seated) My trouble occurs when I try to raise the rpm to balance at about 1500rpm.

The initial pick-up of the engine buggers up the level in manometer such that any balance is virtually impossible. Any advice? How do I adjust the cable ends to begin the procedure? All loose with 1mm of play?

I have also discovered that if you back off the LHS stop screw you run off the TPS range and it doesnt run at all!!

Please resist the urge to be sarcastic as it take too long to read

 

[Blackal]

I take it that the manometer is open-ended?

If that is the case, then you need to bung the open end up with a wad of cotton wool, sufficient to dampen out the initial surge.

Al

 

[ELIMINATOR]

Aren't both ends connected to each throttle body?

 

[Blackal]

Aren't both ends connected to each throttle body?

Might be?

In that case you just need some sort of baffle material in one end to dampen out the pulse.

Al

 

[Spout]

Perhaps the tubing needs to be of greater diameter? and the oil thicker?

 

[roddy]

If your using a u-shaped piece of tubing connected to both TB while doing the balance just put a piece of sponge tyhe same size into both ends of the tubing this is suffient to soften any pulses and stops the oil getting sucked into the engine if the balance is way out.

The stop screws do you mean the ones the cable cam rest's against when the throttle is at rest, if so you shouldn't to touch these.

Once done the brass screws for the idle balance, get your revs to about 3000 and adjust the knurled top screw that the cable goes into then tighten up the locknut a quick check and away you go

 

[littleredrooster]

Get some proper vacuum gauges for about twenty quid with adjustable damping and do the job properly. For best results, bungee the gauges to the handlebars and set the balance under load at about 3500-4000rpm. Then set the brass idle screws, job done. Once you have this set accurately, subsequent balance jobs are a doddle.

 

[jonogs]

Thanks for all the comments guys.... just to follow up...

I reset the cable play at the tbs to 2mm, balanced up fine at 1500 rpm using the manometer. Test ride, bad surging at 2-3K. Re-checked idle balance, still fine. Rechecked 1500 rpm balance, fine. Idle a little high, so reset idle using BBS. Bike now runs fine at all rpm's. Manometer was checked against my carbtune and gives equal readings (if not better).

 

[ELIMINATOR]

I had a play last night using a manometer. Despite having cleaned the brass screws as the inside taper was gunged up, I couldn't get the level in the manometer to equalise, being about 6" out. But bike idles at 1000rpm, wheras before it was 1400. Runs OK. I don't think I'll bother doing the balance at higher revs................. the bike doesn't surge, I don't fancy messing it up.

Only thoughts about balance at idle is that there may be more of the gunge in the manometer take off points. I might get keen & give them a blast with some cleaner.........................sometime

Admitedly the valve clearances were checked about 3000 miles ago, so his might explain the inability to get the manometer reading equal.

I'm correct in thinking that the brass screws only affect the idling, and nothing once off the throttle stops?

 

[jonogs]

Well, that's what i thought until I ran the bike, fully balanced at idle, 1500 and about 3k rpm. The bike surged like never before.

I then rechecked the balance, and used the BBS to wind down the idle speed a little (i guess approx. 150-200 rpm). The bike now idles great with no surging.

As the BBS (air bypass screws) allow air past at idle, they must allow air past at all throttle openings. By adjusting mine it seemed to smooth things out. Of course it could be a complete coincidence

Good luck.

PS My BBSs are both a bit mucky, I have never cleaned them and the bike now has 70k on it. They only really did anything when almost wound right in.