Triumphrat

Hourglassmike · 04-20-2009, 09:00 PM

Just got the Bonneville on the road last week.
I am breaking in the new engine,(so I've been taking it easy,no full throttle Blasts yet.It's a Big Bore Chantland 750 with 932 Amals,Intake manifolds are port matched to the carbs.Jetting on the 932's are 220 main,106 needle jet and a #3 slide.
It feels pretty good so far but I notice when it warms up there's a flat spot just off idle or when I blip the throttle when changing down gears.It doesn't do that when the engine is cold.I'm assuming its to rich,so I started fooling around with the needle position but it doesn't seem to do much.
I've done some plug checks with the needle in its highest position(lean)the plugs are a little sooty at the base of the threads,porcelian looks clean, a little wisp of grey and the electrode Wire has a nice color of blue right at the bend of the wire (Ignition timing is OK).Can anybody tell me what I'm doing wrong, I've tried the needle in all positions and this flat spot is still there and in the same place.It's driving me nuts.
Need Help,
Mike.

Sunshine Jim · 04-20-2009, 09:29 PM

just on the off chance this will help and that it applies to your carbs and that your needle and main are'nt the wrong size and too large...

the throttle slide "cutaway" has a role in carb blipping (throttle response)

maybe that's the prob?

Hourglassmike · 04-20-2009, 09:38 PM

So which way would you think that I need to go?
Mike.

Sunshine Jim · 04-21-2009, 01:04 AM

heh!

well....

i was wondering whether you'd ask that. those slides are in the spendy realm. for the regular amals we could hustle up a buddies and there were enough junk bodies that we had a variety of slides from racing eh?

for each experiment you're talking two slides. just guessing but at least a hunded bucks per set?

so two guesses and i hope if anyone has a better approach they chime in.

A - i figger the guys who reccomended those carbs had a pretty good idea what worked so first i'd call them and get their opinion.

Also pull the plugs one side at time and see if BOTH sides are doing it!

Put the needle back where it was?

i'm guessing they had a pretty spiff cam and valve set up on their test bike and maybe your's is a little fat on the idle jet side. (could be too lean too depending on what you mean by a "flat spot" )

when you lift the the slide the first 1/8 of the carb mix is first from the idle mixture slow jet size, the IMS (idle mixture screw) and the air screw adjustments (if you have one that's adjustable).

the throttle valve cutaway and the main bore size relationship increase their effect as the idle jet influence tapers off

from 1/8 to 1/4 throttle the clip position than the needle taper next control the mix

heres a good picture of the process:

http://www.jba.bc.ca/Resources/jet-chart.jpg

the easy experiment would be to change your idle jet adjustment and than your idle jet itself if it's changeable.

next is the cutaway adjust. you could try a little tape to restrict the opening, if it's too fat that should make it worse

More cut away increases the amount of air in the air/feul mix if you're too fat there. usually while you're actually accelerating not at idle that much. (depends on the carb eh?)

and the Main jet really is'nt the main adjustment till you're at wide open throttle.

take a plug chop at idle, than at 1/8 throttle?

(I'm the worlds slowest typist, that little rant took almost 2 hours to type)

Sunshine Jim · 04-21-2009, 01:30 AM

that's all assuming the throttles are synchronised!

SYNCHRONIZING TWIN CARBS FOR IDLE AND SLOW SPEED RUNNING:

http://www.jba.bc.ca/Bushmans%20Carb...g.html#REBUILD

a little more than halfway down the page, might help in the trouble shooting if the initial synchonization is spot on first.

also if one carb is off and lean it could be a chunk of something blocking the idle jet. i usually turn them all the way in and then back off to where they were if the carb idle is "cranky" if it's a hard 'chunk' that screw will feel different at the bottom (maybe)

if they're still cranky (one side will idle properly, the other won't) you'll have to blow out the jet or remove it (if there is a removable jet)

Sunshine Jim · 04-21-2009, 04:46 AM

i did a little research and found some complaints with some of the 932 Amals.

parts not screwed on tight like the throttle and jet bodies and lots of stray machining swarf and filings in a few of them.

if this does'nt fix easy pop the float bowl off and take a look at everything.

Hourglassmike · 04-21-2009, 09:43 AM

Thank's
I'm not the fastest typer either.I've read the material and thing's are a little clearer now,Thank You.
I'll keep at it and go through the Carbs again and try to pin down where the trouble might be.I have a friend with a bunch of carb parts that he will let me borrow for testing.
I have read your Carb Sync procedure and it Was Better but when the bike warmed up it the hesitation was still there.
Mike

GrandPaulZ · 04-21-2009, 11:20 AM

Mike, whoever sold you the big bore kit should be able to steer you much closer to a baseline carburation setup to tune from.

Carb slides with different cutaway can be sourced for about $25 each. Lots of folks just grind them down, but that's like a manicurist doing metatarsal surgery. If you don't know what you're doing, you're sure to screw it up.

You really only need 1/2 step different slides to find out for sure if it's going to make a difference.

Hourglassmike · 04-22-2009, 09:10 AM

Yes, the slides did seem to make a difference.I took out the #3's and tried 3.5's seemed to respond better .Then it started to rain,and thunderstorm. So I''ll take it out tonight to see if that was the right direction.
Thank's.