Triumphrat

IrlMike

Have a problem with my 98 tbird misfiring when picking up throttle again after shutting off for bend or corner etc

Carbs are Mikuni, with dynojet kit, K&N filter in stock airbox, & thunderbike 3-1 pipe. 2 1/2 turns on pilots

Just rebalanced after problems with misreading tacho (changed to trophy clock set).

All was well for ten miles or so - smooth pickup & good power at all revs & throttle, then problem started. Once the throttle is opened further it runs fine.

New nology & plugs also fitted, valves done.

Carb balance screws seem very sensitive - could they drift off so quick ?

Cleaned out the carbs when fitting the dynojet, tho' missed the inline fuel filter, could this be a problem ?

It's wrecking my head a bit at the moment, so any pointers gratefully received!

patrol21

hmm....the fact this is only happening during cornering makes me think that your not getting enough fuel in the bowls....I would check your filters (in line and petcock)..don't have to pull the carbs so it's a quick one.....your float height might be off a bit also. Did you measure your float height when rejetting? Stock for Mikuni's is aprox 14mm. You might have a float hanging up also...worth a look.

Jimmy900 might be able to really dig into this as he seems to have his finger on the pulse of these carbs.

__________________
The worst day riding beats the best day at work....no exceptions.

IrlMike

patrol21

Thanks for your thoughts there. I maybe didn't explain too well - it happens in a straight line too. The possiblity that the problem relates to low fuel in the bowls has made me remember something else tho'. I sit the tank on a box on a 'workmate' for setting carb balance & did notice through the clear filter I use to extend the fuel line that fuel could be a bit slow flowing thru'.

The inline filter at the carb end (didn't know it was there 'til after I'd refitted carbs!) will need the carbs removed to get at it. I plan to do this anyway, but am wondering if there's anything else I could check, which might give these symptoms, while I have the carbs off ?

I double checked the float heights (14mm), so believe they're ok.

I've heard about slide wear & needle jet wear on Mikunis but don't know what this does to bike running...

patrol21

You don't need to pull the carbs to get at the filter. Pull the gas tank and simply grab the fuel line and pull from the carb bank...the filter is in line. I change mine yearly. It also only takes a few minutes as long as the tank is off and low on gas to check the filters on the petcocks. Did you notice if there was any difference if you switched to your RES setting? There are actually 2 filters (they run separately).

Just a thought...since you were playing with your carbs, etc. and you were running good for a while it almost sounds like you might have sucked a piece of crap into a pilot/main jet. I run some carb cleaner thru periodically and it seems to keep the girls running......

__________________
The worst day riding beats the best day at work....no exceptions.

IrlMike

Ah...ok. Wasn't sure i'd get the line back on....anything I can do without lifting the carbs is good news!

Did you mean go from ON to RES while riding ? Didn't try that....but when I thought fuel flow was iffy when balancing carbs, I did then - no difference. Also tried draining into a can - plenty of flow. (Had too much fuel in the tank at the time to drain off & check tap filters...)

Thanks patrol, the more I think about, that inline filter has to be prime suspect - will be on it tomorrow am !

patrol21

Hi Mike,

I have just installed a dynojet kit on my 95 bird w/Mikuni's. I have been tweeking the settings as I was hitting a wall at 4-5K but from what I have been seeing this is not uncommon as I replaced the stock filter with a K/N and cut a bunch of holes in my airbox. I have since taped up all but a matching one that is on the opposite side of the box to the stock one. I have not had a chance to check this as our weather is snowy right now and I have unrestricted Tiger rubbers on order. Here is my current setting

K/N replace
Stock headers with Emgo silencers
Dynojet needels @ 3rd clip
Mains-dynojet 98
floats 14 to 14.5mm
pilot setting 2 1/2 turns

Once I get the rubbers from Bike Bandit and get them installed, I am hoping covering up most of the holes will solve my mixture problems. Any problems you ran into with your conversion?

__________________
The worst day riding beats the best day at work....no exceptions.

IrlMike

Hi Patrol,

No, I'm sure my 'off zero throttle' misfire is not related to to the fundamental set up. Until this problem had developed it was sweet & pulling like a train at all revs & throttle, with a 19t sprocket too. I had a swop with a fellow rodent's 98 TBS last weekend for ~ 25mls. I thought performance ~ same - he thought mine was quicker. His stock 6 speed setup is ~ 2 or 3 % lower geared, so maybe I do have a little more torque/ power.
My only other tweak is to file the ignition pickup mount holes to give ~ 2 deg more advance - my calc is .65mm 'circumference' length per degree.

I'm of the opinion that the stock airbox (with a K&N) is the easiest way to go for strong low & midrange torque, while getting more top end - this is what the TBS has with it's extra 14 hp. The other (only) key difference with TBS is the exhaust balance pipe fitted at the muffler end. To me, this makes it look pretty much like the 3 into 1 I have. I suspect this is very significant - improving 'scavenging' - tho' I'm totally the amateur engineer here. (Have electrical eng. BSc but not much help with this !)

I'm not familiar with the emgo pipe, does this use the stock headers ? If it does, it might just be different enough to mine (or a TBS) to need a slightly different carb (or airbox hole?) set up.

BTW, I've just ordered an optional baffle, 'DB Killer' <not too much I hope > from Thunderbike, & noticed they have a special offer on just now.....good value imho, tho' still bucks alright.

I tackled the 'duckbill' filter this morning & found about 1/8 of crud filling the bottom. Didn't look that much, but when I connected my remote tank set up to recheck carb balance, the flow through the clear filter was massively more rapid than before. So, I'm hoping....not tried it out yet as weather's a bit rough here too.

patrol21

Hi Mike,

I think you might have found your gremlin.

To be honest, it if wasn't for the fact that the older TBirds had the paint in the tank issue from the gas spout, I might even ditch the in line filter as the petcock is already filtered with the same fine screening. Seems a bit of overkill. If it wasn't for the fact a replacement is a couple of bucks and it's a quick fix, it be in the trash.

Anyhow, I hope this fixes your issue.

__________________
The worst day riding beats the best day at work....no exceptions.

jimmyj900

Take a look at your needles and needle jets next time you pull the carbs out.

The Mikunis have a problem with wear on the needle jet that richens the mixture too quickly when the slides start to lift, so look shiny areas that indicate rubbing.

Jim

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IrlMike

Hi Jim,

Thanks for your post there - I still have the problem

It sort of seems to come & go a bit in it's severity, from hardly noticeable to pretty awful, but it hasn't gone away. A pity, as this was otherwise a great set up.

I'd read about the needle & needle jet wear & took a look at Factory Pro's site info. The original needles were showing signs of wear. I looked at the needle jets under an illuminated desk magnifier & they +seemed+ ok, so I put in new dynojet needles & hoped I'd be ok - looks like wasn't. I guess you are confirming that ? - good to know, thanks.

Feeling a bit loathe to be buying new parts for these mikunis to last how long (?), I took a look on ebay & my luck was in, just bought a set of Keihins off a legend for ~ $150 . I plan to keep this (awesome!) bike for a long time, so it felt the right way to go. Taken a bit of a hit on the new dynojets & tiger rubbers, but will post these up on the classifieds & see if anyone wants...we live & learn

I'm thinking I should be ok with stock jetting for now on the Keihins with K&N in stock airbox & thunderbike 3-1, but looking at your previous posts (& others too) I think I'll want to play later with some mods & factorypro or thrux needles

BTW, you recall I was having carb setup problems with tickover speed ? Turns out the tach was faulty, high by 3/400 rpm - now have a trophy clock set (ebay 40 bucks! -complete with water temp gauge) & no probs carb setting..

Cheers,
Mike