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Discussion Starter #1
Hi all,

So, I'm currently in the process of rebuilding an S reg carb speed triple 900 (mark 1) but I'm having issues getting it to run again. No doubt it's something I've done as it was running before but now wont fire on cylinders 2 and 3. Number 1 cylinder is firing but I cannot isolate what is causing 2 and 3 to not fire.

I have gone through the whole process of checking everything so I have checked spark plugs, ht leads, coils, side stand switch, cam position sensor and all ok and working as normal. I have checked the routing and connection of the electrical wiring to the number 2 and 3 coils and both are fine and correct.

The carbs are spotless and have been ultrasonic cleaned and also been upgraded with a factory pro kit, so the main jet size have been increased slightly. In addition I have fitted pod filters to this and removed the Airbox and snorkels completely.

My thinking is now drawing me towards it being an electrical issue as when trying to start the engine it turns over but for whatever reason it simply wont fire on number 2 and 3 cylinders.

Any help would be greatly appreciated and more information can be provided on request!

Cheers
 

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Like you said ... sounds electrical, so plugs - leads - coils - igniter and all the connections between them. I’m no expert but from what I’ve read on here the coils are a recurring issue. Maybe try swapping the coils between cylinders and see if the problem moves accordingly....
 

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Discussion Starter #3
Like you said ... sounds electrical, so plugs - leads - coils - igniter and all the connections between them. I’m no expert but from what I’ve read on here the coils are a recurring issue. Maybe try swapping the coils between cylinders and see if the problem moves accordingly....
Hi,

Thanks for your response! So I have had a good look through the wiring and nothing looks obviously wrong.

I'm now even going as far as putting the carbs back to stock main jets/airbox as that was only main thing I really tried to upgrade. So part of me wonders if it is simply over fuelling and cannot handle the jetting size increase.

I will try this and failing that the coils may need to be replaced to check as well!

I will post further updates after this has been done!

Cheers
 

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I have Factory Pro jets in the Mikuni carbs on my ‘95 900 Sprint and I’m using a Ram Air filter in place of the Triumph air box and snorkel set up. I’ve not had any issues like you’re experiencing. I’ll see what size jets I’ve got fitted and report back.
 

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Discussion Starter #5
I have Factory Pro jets in the Mikuni carbs on my ‘95 900 Sprint and I’m using a Ram Air filter in place of the Triumph air box and snorkel set up. I’ve not had any issues like you’re experiencing. I’ll see what size jets I’ve got fitted and report back.
Perfect! Let me know how you get on, I will try rebuild the mikuni carbs on mine this weekend and feedback the result also
 

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It's an electrical problem. Is # 2 & 3 coils getting 11 - 12 volts when you turn on the ignition key? Of the two wires going to the coil one wire will be feeding 12 volts to the coil, On my bike it is the green wire but your harness may be different. If you look closely there should be a + on one the the spades coming out of the coil. That's the terminal the 12 volt wire goes to, but the engine will run just fine if the 12 volt wire is on the other spade. If you get a voltage reading less than 11 volts it is time to consider switching over to the Johnson Jolt. It's easy to do, you'll just need a, extra relay.
 

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Further to earlier posts, my carb set up is as follows:

Pilot jet 045
Needle Jet 615-08
Needle 5F21
Main Jet 135
Air Screw 2 turns out

I’ve also drilled the plastic slides (drilled one on right in the pic)
718347
 

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that is radical use of the drill. I will be following the first ride with interest. I imagine you don't have any running impressions of the engine yet?
 

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I fitted a Factory Pro kit and drilling the slides was specified in the kit instructions. The engine runs well and picks up with no spluttering or flat spots... however it’s only been run with the bike stationary.. might be a different story once it’s under load.

My understanding is that the drilling causes the slides to rise more slowly and increases air speed through the venturi.

I have a spare set of slides just in case 😁
 

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Discussion Starter #11
So! Its been slightly longer than the weekend but I've had a tinker.

I have removed the factory pro kit from the carbs and gone back to stock main jets. I have also changed the spark plugs (again even though these were new) and the bike starts up on the button with no coughing or spluttering at all.

I can only assume I must have incorrectly set up the FP kit and it was over fuelling as the carbs were swimming when removed after all the failed attempts. I have unwrapped the main loom to check all wiring and all seems ok, although I will re wrap this and see if the problem comes back.

All I can say is thank you to all for your input it has pushed me in the right direction to getting the bike running again. I may well speak too soon as the build is still a few months off finishing but I will update progress on it again shortly
 

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Great to hear and helpful too to get a result. I drilled the slides the same as you on my Daytona 900, following DynaJet kit instructions. That was years ago. That ran very rich too but turned out was mainly because I'd over oiled the KnN filter. I wasn't happy with the kit though so switched to the John Fitzwater recommendations. Very happy afterwards. The drilled slides are still there and in fact I subsequently did the same with my trophy 1200. Seems to help with hesitation around 3000rpm.

I look forward to more updates!
 

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Sorry - he was the guy behind the original Hinckley FAQ, via his new Zealand Thunderbike business.

I've just seen the link on this forum was broken again so put one in to the waybackmachine, here for your convenience and edification:


Look at the jetting table 6.1.2 "Hot setup"
 

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This is the jetting info in words. The "John" quoted is John Fitzwater:

6.1.2.4. What about just massaging the jets and not going for the expense (and drilling) that a jet kit requires?
This, also from John, is golden information, a veritible Holy Grail for do-it-yourselfers. (It is the 'HOT SETUP" above.) Thanks John!

"FWIW, on a stock bike, you can get very good results by reworking the stock jetting.

Triumphs triples have a characteristic downward bilp in the power curve at 4800 rpm. You can fill this in by lifting the needle to the 5th groove from the top (ie bottom groove) and fitting a couple of Dynojet style needle shims under the clip. This will give you about 4.5bhp increase at 4800rpm by filling in the hollow.

(Air mixture screws should be turned to between 2.5-3 turns out, or, more specifically, 3 percent co, measured using an exhaust gas analyzer tied into the header.)

We take the centre mains out to 125 and the outer cyls to 130 - this will give you about 1.5bhp at 8-9500 rpm. The good bit is it costs you almost nothing other than time."
 

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Here's the best carb explanation I've come across. CV Carb Tuning Procedures
I owned a 1996 900 Trophy with stock exhaust for many years and fiddled with the carb quit a bit. 125 main jets in all 3 carbs worked the best. Different mufflers might need you to change the main jets. This is what I found. Take the bike up to 100 mph in fifth gear. You should feel a difference from going 3/4 throttle to full. If it pulls away going to full throttle, good. If it doesn't the main jet is too small. As for the needle setting. Take the bike up to 40 mph in 2nd gear, then whack open the throttle. If the engine hesitates or stumbles the needle is too low. If the engine takes off, good. As for the idle screws. Blip the throttle at idle, if the idle speed drops below the idle setting the mixture is too rich. If the idle speed hangs up and then slowly drops back down to the idle setting the mixture is too lean.
I wish you good luck. I found a MotioPro bevel gear screwdriver most helpful in turning the idle screw, they cost around $100.
 
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