Finally changed my main jets - what to look out for?

[vecchio lupo]

Even a stock bike could benefit from a set of 115s over the 110s that come standard, especially if the air induction has been circumvented.

Yes, this is a slow board, but a thorough one without all the "Who shot John" that comes standard with huge boards.

 

[fordtech48]

ok, here's some questions for the carb gurus. Got my carbs off and partially disassembled. The p.o. had dynojets installed at dealer when he purchased new(have the paperwork). They did this when installing the staintune mufflers. Air intake still all stock. Then he had it to another Triumph service shop complaining of stalling, bad hesitations and some other running issues at around 2000 miles. They went through the carbs again but not sure what they did. The p.o. told me when I bought it they "went back to Triumph " parts and he hadn't had any running issues.

Fast forward to today- got the carbs off and apart. Pilots are 42 and mains appear to be 118. Can barely make out the first 1 on the 118 but the 18 is clear.

I also noticed inside the area in the top of right side carb was very carboned/sooty. The left side was clean in this area. Also, the needle has 5 grooves and there's a clip in the center groove. Also- 2 small washers (shims?) on both. The weird thing- one of the shims on the one carb was above the plastic insert in the slide- on the other carb both were under the plastic insert on the needle side. (if that makes sense). Are these dynojet needles? Do the stock needles have these grooves? I think this must have been an issue.

Also- the one slide rubber diaphragm was smooth while the other was wrinkly. didn't seem right. Also- the one slide is shiny and one is more carboned-darker looking on the aluminum slide area.

When I bought the bike it ran decent- had some stalling issues when idling and if throttle was blipped would stall. Keeping the idle speed at 1100 seemed to take care of that-(1100 is too high- should be 1000) MPG wasn't great- around 36-38- seems low. Also the enrichener had to be pulled for a while or bike would hesitate- stumble.

The last couple times I ran her in November the bike sat for about 3 weeks- was very hard to start before work one morning. Needed a lot longer "choke" than usual too- it was a little colder.

Figured I needed to start the bike every week or so in the winter and added stabil to the fuel. When it got around 40 degrees or less the bike started running ok with the choke pulled but would backfire and run like crap if throttle opened. I figured the heck with it and drained the bowls- gas was clean- and let her sit through the winter.

I want to get her running right- so what suggestions, info can y'all provide based on what I have found? Thanks, FordTech

I will try to attach some of the photos I took.

 

[B06Tang]

Before diving into this too deeply but were there caps on these before hand?

 

[fordtech48]

Yes, The vacuum caps were on there. They were starting to crack but don't think they were leaking. I have replaced all 4 caps- AI was removed previously.

I have since ordered stock (NBZT) needles and new bowl gaskets, and 4 new intake O-rings- although they still looked ok.(no deformations or flattened out) The carb had dynojets and 1 carb had 2 shims ABOVE the clip and 1 carb had 1 above and 1 below the clip. ?????? what were they thinking???

Cleaned the carbs real well- someone told me soaking in a 50-50 mixture of pine-sol and water worked great for soaking carbs. I'm here to say - that is a great idea and works! Carbs weren't all that bad to begin with but came out like new. Took them to work and cleaned them with mineral spirits in the parts washer for good measure and blew off with compressed air. Also, polished the slides real well. Carefully cleaned and inspected the diaphragms and they appear to be ok.

Trying to decide on what jets to run.

Had the stock filter with snorkel removed. Staintune mufflers. right Plug is black and sooty upon inspection- although the last couple times bike was run outside garage for a short time and was running like crap. Right carb had carbon from backfiring and I haven't checked the left plug yet. (looking at the photos again- it was the left carb that is sooty and the left cylinder that was backfiring) I need to check that plug to compare to right side.

Side note: these plugs are not standard 5/8 or 13/16 spark plugs. They appear to be 18mm hex. I took the right plug out with a 3/4 deep socket and it was loose so I think they're 18 which I didn't have at the time.

Originally the carbs were 42 pilots- 2.5 to 2.75 turns and 118 mains with dynojets and shims.

My biggest question is whether to stick with 42 pilots or go back to the stock 40's? I think the 118 main may be ok -not too rich but not too lean. I don't want to run too small a main. I think my mid to top end was better than my low to mid. If the 42's were too rich would that account for the not so great low to midrange? I would like to not have to take the carbs back off if I can help it. I also drilled my slide hole to 2.76 mm-(7/64 bit)

Also, I regapped the pickup to .8 mm from 1mm and added a Nology pro-fire ignition coil. I'm replacing the plugs too. The bike had the stock air filter and I'm adding a K-N.

Anyone with an opinion feel free to give it. Thanks.

 

[2Monkeys]

The stock answer to all jetting questions is "you should check out jenks bolts tuning guide."

The needles you had in there were definitely dyno jet.

With staintunes and an intact airbox I would absolutely go back to 40 pilots, stock needles, no shims(maybe one shim but start with none), and as many turns out as keeps the popping on over run to a minimum . Gotta balance the carbs too. Thats my opinion for what it is worth, ya did ask. Best of luck.

 

[fordtech48]

The stock answer to all jetting questions is "you should check out jenks bolts tuning guide."

The needles you had in there were definitely dyno jet.

With staintunes and an intact airbox I would absolutely go back to 40 pilots, stock needles, no shims(maybe one shim but start with none), and as many turns out as keeps the popping on over run to a minimum . Gotta balance the carbs too. Thats my opinion for what it is worth, ya did ask. Best of luck.

What exactly causes the decal popping? Too lean a mix? My airbox is intact but no snorkel and k-n filter.

I was thinking keeping the 118 mains and trying the 40 pilots at 2.5 turns out to start with. I'm going to check the balance too- working on a homemade manometer.

What is the reason to go to 42 pilots? to enrichen the mixture only? Or is there some other reason?

Thanks for your time and advice.

 

[2Monkeys]

Yeah the overrun popping is just a little leaning out which, from what I have read, having a little is fine. If you have the air injection system still installed the popping will be worse. Seems like most get rid of the AI and have occasional popping on overrun.

The K&N and the snorkel out don't gain you much on the intake side. The real regulation there is the restrictor plate inside the airbox, that is the boss on how much air goes thru right up until you remove it so the motor can breath better. Lots of threads on the assorted Bonneville forums about that.

Yup the 42s are to give more fuel at idle and partial throttle, though that is all regulated with the number of turns out your mixture screws are at. 42s and 1 turn out should probably bump down to 40s; where as 40s and 3.5+ turns should think about bumpin up to 42s.

What exactly causes the decal popping? Too lean a mix? My airbox is intact but no snorkel and k-n filter.

I was thinking keeping the 118 mains and trying the 40 pilots at 2.5 turns out to start with. I'm going to check the balance too- working on a homemade manometer.

What is the reason to go to 42 pilots? to enrichen the mixture only? Or is there some other reason?

Thanks for your time and advice.

 

[fordtech48]

Ok, that's what I thought. My 42's were at 2.5-2.75 turns out(not my settings- this is how the bike was when I bought it). I never experienced any popping back on decel. I'm not sure but I don't think they are Keihin 42 pilots. I say this because the on the other pilots I have there is a K symbol.

Based on Jenks guide I am thinking 120 mains, 40 pilots. I really want to have this right so I don't have to redo the pilots. Mains would be no biggie on the bike but pilots would be a different story. I was thinking 1 shim but now not so sure if I should add a shim.

What is the main difference between 1 shim and none? What range does this affect most?

One more question about shims. Why is one side seem to be ground while the other side doesn't? Which side faces which direction? I was only thinking I should use a shim because of the longer NBZT needle to get it out of the main some.

 

[2Monkeys]

Yeah I'm not surprised you never had popping on overrun with the 42s in, that set up looks like it would be rich at idle and partial throttle to me.

The shims are just spacers I don't think it matters which side is up or down, I would just be consistent in which way I placed them. The shimming effectively adjusts the transition between just pilots and pilots+mains. The shims are fairly easy to add when you are trying it out and dialing it in.

One other thought: look at the springs you have and make sure you are using the stock springs with the setup you are talking about using. Dynojet springs are much lighter gauge than the stock ones. I would use all stock parts or all Dynojet parts, mixing and matching is going to be nothing but a headache.

 

[bonZa]

I'm going through my carbs soon and have a question.

The Triumph manual says the 790 and 865 Bonnie mills both use 110 main and 40 pilots. Would this be correct? I woulda thunk the bigger engine woulda had bigger jets. Maybe a typo? Any help appreciated.

Also any suggestions would be nice too. I'm running stock airbox with K&N filter and Staintune Mufflers with baffles installed. Thanks.

(didn't mean to hijack the thread)

I have similar set up to you, Dominator mufflers (same as preds), snorkle gone, free flowing filter but the airbox is intact

have size 40 pilots, mixture screws out 2.5 - 2.75 turns, 120 main jets, Thruxton needle (NZBT) with one shim and idle set at about 1100 rpm

I also make sure the carbs are balanced and the bike runs fine, no popping on decelleration and it accelerates to 100 mph very quickly, which I did today
the shim affects the mid range I think and all I know is I have no hestitation or vagueness at this position

it is easy to try just by trial and error, which is what I did, plus used the Jenks guide as a baseline to work from

 

[fordtech48]

2monkeys, yes I have ordered new springs to be sure they are the stocks and not dynojets. I also ordered new orings for the pilot screws. They are actually kits with a new spring, washer, and o-ring for each screw. Wanted to make sure I had no leaks. I got the kits from CVperformance. I'm still waiting for them to get here.

Bonza, I will try one shim and see how it feels. I also drilled my vacuum slide holes to 2.76 mm (7/64). 1100 seems a bit high for idle. Will it not idle smoothly at 1000? Just wondering. Maybe go out to 3 turns on pilot screw.

Thanks guys for the suggestions.

 

[vecchio lupo]

My seat of the pants dyno and old school Dark Art of carb fiddling showed me that 42 pilots and 140 mains was a little wet and sluggish at top end, and 135 mains seemed about right. While in Daytona I sprung for a tuning session at Triumph of Daytona. I was right that 140s were too much, but the 135s were falling a tiny bit flat at full on power.

Final result: 42 pilots, 137.5 mains, 3 turns on adj screw and 1 shim on the needles.

She pulls smooth through transition off idle with no noticeable step and rockets up to 100 mph then walks up to 110 mph indicated. She might have a couple more MPHs in her but I don't anymore. Again, an 03 790cc with AI, air box removed. Pods and Toga exhaust. Also aluminum intake manifolds from TPUSA.

I now get all the gas I can burn and only burn the gas I get.