Bonneville America Forums Forums Technical Forums Performance Mods Shimming Question

Here's my deal. I did the airbox cutout on the bottom, have 135 mains. My bike ran great until I desnorkeled it.Then my bike started to backfire on decel again when I desnorkeled it so I ordered some shims. I have 135 mains. I also have a K&N airfilter I was getting ready to mod and put in but am afraid to do it now. I pulled my needles out and there were two large brass shims already in place!! I went ahead and put in the 1.5mm shims my shop shipped to me. Did I f$%k up? Or do some models come with these big brass shims already in place? Please help......

None of these bikes come with shims, steel or brass. Someone had to have added them.

What are your air mixture screws set to now? I'd try adjusting them out about a half turn and see how she runs.

On the shims and out of curiosity, how thick were the brass ones? Personally, I would try to get the bike within good running conditions with no shims and work with the jets to start. The shims are more of a fine tune.

Uhhh. Your gonna have to provide more info. At closed throttle on decel you are in the idle circuit. Try moving up to 45 pilots. Some gurgling on decel is normal- in fact, it is desired. Popping and backfiring is not. There is a brass part in the needle circuit It is sorta oval/round and goes between the mains and the needle jet, but that is only accessable from the bottoms of the carbs. The shim goes on the needle in the top of the carb. Shim/needle/chair/spring/lid. You are working in the top of the carb, aren't you? take a browse through this link at Pat's site...

http://www.dinqua.com/Triumph/Shim1.html

I know those may sound like stupid responses, but I not sure where you are at in the process and I don't know the history of your bike or you knowledge/skill of carbs. Please be patient...

Phil's answer is right on for the tuning... I gotta know about those shims

Agree with Erwin and above. I have my airbox bottom removed also. No carb needle shims at all. Idle air mixture screws at 3 3/4 out-that is key to reducing popping on decelleration. Now running TBS needles, but stock needles were fine also, jut TBS needles give it a little more power.

What pipes ya got? Start with the screws, that's free. Then maybe try some 45 pilots, that's cheap. Then get a freak and pipes, that's expensive

Benny,

Lets backup, you have to explain in detail everything you have done so far to the carbs.

Did you pull the bowls off and and mess with the jets ? There are several small parts that need to be put back in order and they are very easy to lose (don't ask me how I know).

You have to be extermly carefull when you pull the caps off to get the needles the rubber diaphram has to be seated correctly or you are going to get the results you are speaking of. Follow Pat's instuctions and make sure they are seated correctly.

The big brass shims were right underneath the needle head, accessible from the top of the carbs. I had to reseat the rubber diaphrams when I pulled the needles out and it was a bugger!! I did take the bowls off the bottom to replace the main jets, and one of the pieces you speak of came out with one of the jets, but I put that back in. The big brass shims I am speaking of are accessible from the top. They are maybe 3-4mm thick. I don't know crap about the mixture screws you guys are talking about, could you fill me in? I am going to Dinqua's site to check that out too. I have TOR longs on my bike. I am not even sure if my bike has 42 pilots now, it had 125 mains before I changed to 135s. So you guys are pretty sure someone tweaked my carbs before I got the bike?

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So you guys are pretty sure someone tweaked my carbs before I got the bike?

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Yep, 120 mains are stock and no shims. You need to check your pilots also.

Right behind the two connectors on the carbs are the air mixture screws. Remove the connectors and use a small mirror to see up into the tube. You should see a D shaped head of brass.

How many shims some of you use on the stock needle to comply with airbox mods/or freak and pipes?

I put it back to two shims, K and N , and plugged the hole in the bottom. It runs better now.
thanks guys!!!

I've seen that to stop AI system without dismounting everything is very easy.

There's only to remove from the left carb's manifold a rubber pipe that goes to the pulse air pump and put a piece of closed black pipe.

The pipe can be closed with epoxy bi-component glue. Oher glues get melted by gas.

Or ask to the dealer for one of that blind cap like the one on the right side.

There's another way, putting a piece of black (thermoresistant) pipe instead of the right 2 caps on the right manifold and right carburetor, so you can have two caps to use like you prefer. One on the left manifold to stop AI and close hose, and one spare to save.

That's until you do carb syncing, you'll need the spare cap again because on right side you'll need to remove the pipe and close one side.

Without pulse comeing from manifold the AI stops working.

What about two shims?
Do you notice some pops on decel at mid range with closed throttle?

Have you tried more shims?

In every mods I did to my previous bikes I saw to accomplish an airbox mod and have the same results of a Dynojet needle On the stock needle I needed 4x 0.5mm shims (1/12") and sometimes 5 or 6 shims (1/10" or 1/8").