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Discussion Starter · #1 ·
Bike is a 78 Bonneville, with electronic ignition. Bike runs great, starts first kick almost everytime, give it a couple of minutes to warm up with the choke on and she idles good. Here's where it gets weird. If I go for a ride, no matter how long or short, and I stop somewhere and turn the bike off, whenever I go to start it back up, it fires right up, but won't idle worth a shit. It will stall out without throttle. I'm totally confused by this, because it runs great and idles fine up until then?? Any ideas?
 

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Heat soaking the carbs boiling the fuel in the bowls until you get fresh cool fuel in there. Modern fuels aren't anything like we're used to.

I've got the same issue with some old Jags.
 

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Discussion Starter · #4 ·
Heat soaking the carbs boiling the fuel in the bowls until you get fresh cool fuel in there. Modern fuels aren't anything like we're used to.

I've got the same issue with some old Jags.
I was leaning toward that direction too, like the fuel nearly vaporizing or something along that lines. Anything I could do to remedy that?
 

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You could start with a phenolic spacer on the carbs to isolate the bodies from the head. It's a lot more likely to be transferring heat there than radiant heating. If it is radiant there's tonnes of heat shield fabrics being sold in the racing community these days. How about some aluminum foil around the fuel bowls for a quick and dirty test? Don't forget the fuel lines...
 

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You could start with a phenolic spacer on the carbs to isolate the bodies from the head. It's a lot more likely to be transferring heat there than radiant heating. If it is radiant there's tonnes of heat shield fabrics being sold in the racing community these days. How about some aluminum foil around the fuel bowls for a quick and dirty test? Don't forget the fuel lines...
+1 on the spacer. had a BSA m20 that did the same thing.
 

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You cant fit phenolic spacers to a stock 78 T140, amal MKII's don't bolt up to a flange, they are attached with a short hose or rubber like a Mikuni, so they rarely have temperature issues like the concentrics.
Sounds like you are looking in the right area though, sounds carb related, but if its a boyer, try swapping the box and check the voltage to eliminate that if you can.
 

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you don't say what carbs you have, if you have the Amal mark II's they have issues with the enricheners leaking and making a warm bike run like shit. enricheners are a whole separate fuel supply making for a richer mixture, a choke reduces (or chokes) the air supply making a richer mixture.
if you have the earlier Amal mark I carbs, many people don't realize that you pull the choke lever and it pulls the chokes to the off position, and then push push the lever to put the chokes in the on position.
 

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Discussion Starter · #10 ·
I have Mk2 Amals. I don't believe it's the choke not fully closing. I could ride for thirty miles with the bike up to temp and it runs great. it's only when I stop and get back on the bike that it won't idle. Even then it starts first kick and runs fine, it just won't hold an idle.
 

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here is a Triumph service bulletin about an issue with the linkage not allowing the one on the right side not to close all the way, and if that doesn't work you will likely need to change the enrichener plungers or the rubber seals out for new ones....
 

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Discussion Starter · #12 ·
I've seen that service bulletin before, my carbs are less than a year old brand new, and I'm still skeptical that if there was something up with the chokes that the bike would run crappy nearly all the time, not just after restarting it after a awhile. I'm not discounting it, but like I said, just skeptical.
 

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When the bike is about to die is there black smoke? Have you pulled a plug when this happens to take a looksee if it is running lean/rich when this happens?
 

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Discussion Starter · #15 ·
No black smoke or any other indication that something is wrong, it just won't idle. its a pain in the ass coming to a stop and only using the rear brake so you can rev the motor, or having to upshift to 4th and bump start it because it stalls.
 

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the Amal mark II's strike again.
if you got good ones great, if you got bad ones, good luck.
We have had two sets here at the shop on bikes that have rebuild, choke replaced, jet corrected, slide corrected, and rubbed on by every Mark II profesional out there and they run like shit foul every plug you stick in the motor.
at some point you may need to give up on them and throw a set of Mikuni's on it.
There is an ongiong 200 page thread on the BritBike forum about trying to get them to work right.
Sorry, but IMO I dislike the Amal Mark II more than I dislike Mikuni's.
 

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A friend had the same problem, when he opened the gas tank it released the pressure"vapor lock" doen't hurt to start it up and open the tank see what happends. I've had very good luck with the J.r.c. carbs btw
 

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Discussion Starter · #19 ·
Thanks for all the tips so far guys. I've considered Mikuni's before as well, now I'm going to consider them even more now, haha. I will try relieving the "vapor lock" with the gas cap and see what happens. No fuel leaks, and it basically needs to sit until its back to whatever ambient temperature it is that day. IN other words it needs to cool off completely.
 

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If it needs to cool off then yes, it's a vapor lock issue, are your fuel lines close to the head? I mean like less then a inch? also what type of fuel line are you using? If it cheap line it could collaps due to the warmth of the engine and pretty much starve your engine at idle. one more thing I've had this happen, my inline fuel filter was clogged, and my triumph would not idle, but it would go when I have it a fist full of throttle. just some ideas, hopefully not too much info
 
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