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Discussion Starter #1
Thought I would float this out there being it’s a rainy Sunday afternoon on the east coast of the US. A little background, 1968 Bonneville, 2000 miles on a complete stock rebuild, 932 Amels, running points, just charged battery to be sure. Took a ride last week and ran it up to about 80mph up a long smooth hill and at just a little over 80mph it started cutting out so I let off it. For the rest of the day and still it acts like there is a “dead spot” in the throttle where it lags and you need to push through that spot and then runs normal. I’d say it’s at about the halfway point or a Little less. And it feels kinda like your driving into the wind, like your pushing it a bit more than usual. So any ideas of where to start? Oh and fresh oil change to 20-50 V-twin oil if that is a factor.

Steven
 

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Discussion Starter #5
Sorry for the lag time in replying, that job thing always gets in the way of bike stuff. Well got her out for a little 40 mile run, filled up the tank and it felt about 80% better. So I’m thinking bad fuel could have been the culprit? As for jet size I didn’t set it up I bought this bike “restored” so I haven’t messed with much and still have a lot to learn. Stock pipes, also what was the stock size carbs? Thanks for the replies so far. Next plan is to take back to the shop that built it along with a good bottle of Sapphire Gin for the builder himself and look over his shoulder and ask a list of stupid questions. Was going to ask about cleaning carbs, adjust valves again and timing due to popping through the carbs at times and not as peppy and the throttle once was. And thanks for the title edit also...

Steven
 

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Discussion Starter #8
Interesting Bob.... I’ll try that. One thing I noticed today before a short ride. Tickle the left carb... 1,2,3 fuel. Tickle the the right it’s 1,2,3,4,5...6 fuel. That’s with a 3/4 full tank. So I’m guessing one passage or another is restricted?
 

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Slow tickler action is usually caused by the roll pin being pushed too far up into the bottom of the tickler button. Sloppy assembly at the factory. Can you feel the fast tickler contacting the float earlier in its stroke?

If the float bowl is removed, the pin can be pulled down a little bit, with pliers.
 

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I've certainly had flat spots in carbs before - usually caused by running lean on purpose at certain throttle positions due to US EPA regulations. A little rejetting usually sorts that out.

Also had a bike cut out on an LA freeway due to high speed fuel starvation. Great fun.

In your case, you say that it started during hard running and then stayed that way. I kind of wonder if you sucked up some particle of dirt, and it's worked its way loose now?
 

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Discussion Starter #11
Work has kept me from playing this last week but I did manage to get a quick ride in. And I tried the 2 open petcocks and it seemed to make a difference. I’ll try it again and run some sea foam or the like and see if a good stiff beating for 50 or so miles helps before I start taking things apart.
 

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If you float bowls have drain plugs, drain them into a container. Open fuel taps one at a time to verify decent fuel flow from each side. Verify gas cap breather is functional. Verify air filters are clean.
 

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Thought I would float this out there being it’s a rainy Sunday afternoon on the east coast of the US. A little background, 1968 Bonneville, 2000 miles on a complete stock rebuild, 932 Amels, running points, just charged battery to be sure. Took a ride last week and ran it up to about 80mph up a long smooth hill and at just a little over 80mph it started cutting out so I let off it. For the rest of the day and still it acts like there is a “dead spot” in the throttle where it lags and you need to push through that spot and then runs normal. I’d say it’s at about the halfway point or a Little less. And it feels kinda like your driving into the wind, like your pushing it a bit more than usual. So any ideas of where to start? Oh and fresh oil change to 20-50 V-twin oil if that is a factor.

Steven
Hi Steven
Your initial description worries me a little, apart from the main jet working loose or the inlet tract developing an air leak, I find it hard to think of anything that would occur with the carbs mid ride, that would give you these symptoms.

On thing that you did mention is that you are 2000 miles from a rebuild. If I was in your position I might be tempted to make a couple of precautionary checks before I dived into the carbs.
If you have points ignition and they were replaced at the rebuild, I would quickly check the ignition timing to see if it is retarded. When points are renewed the heel on points need to bed into the points camshaft. Initially there is a lot of wear on the heel causing the points gap to close up, then this settles down to a very small amount once the bedding in process is over. 2000 miles a reasonable time for this to be checked.
If you have electronic ignition then ignore this.

2000 miles is also a good time to check head torque and valve clearances, where they have settled down after the initial build. If a valve is not closing fully you will get reduced performance.

I would also check that the main jets are still in place and for air leaks at the inlet manifold.

These might be perfectly fine, and they are only 10 minute checks, but if they are not right you could waste weeks chasing a perceived fault in the carbs.

If you get to the point of checking the fuel flow, I would be happy if I got 300ml per minute from each float bowl drain with one tap open and half a tank of fuel.

Good Luck
Peg
 

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Discussion Starter #14
New British made cap, new air filters 2200 easy miles on them. Opening both petcocks did make a difference for sure. But as you said I suspect it’s ready for a points, valves and carb adjustment. Don’t shoot me but I took it back to the shop where I bought it at 750 miles and he went through those adjustments then. He did tweak the timing a bit and I didn’t like the way it behaved after that. Sort of lost that snap when you touched the throttle, actually put almost a lag time in it. So I’m going to take it back this week and try and learn a few things. Like I’ve said before this is my first Triumph and I know enough to know that I don’t know. So instead of screwing stuff up right out of the gate I’m going to watch, read and learn a bit on carbs, valves and timing before I get in there and mess things up. Thanks for all the reply’s and knowledge shared, I’ll let you know what I find.

Steven
 

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Hi Steven
Your initial description worries me a little, apart from the main jet working loose or the inlet tract developing an air leak, I find it hard to think of anything that would occur with the carbs mid ride, that would give you these symptoms.

On thing that you did mention is that you are 2000 miles from a rebuild. If I was in your position I might be tempted to make a couple of precautionary checks before I dived into the carbs.
If you have points ignition and they were replaced at the rebuild, I would quickly check the ignition timing to see if it is retarded. When points are renewed the heel on points need to bed into the points camshaft. Initially there is a lot of wear on the heel causing the points gap to close up, then this settles down to a very small amount once the bedding in process is over. 2000 miles a reasonable time for this to be checked.
If you have electronic ignition then ignore this.

2000 miles is also a good time to check head torque and valve clearances, where they have settled down after the initial build. If a valve is not closing fully you will get reduced performance.

I would also check that the main jets are still in place and for air leaks at the inlet manifold.

These might be perfectly fine, and they are only 10 minute checks, but if they are not right you could waste weeks chasing a perceived fault in the carbs.

If you get to the point of checking the fuel flow, I would be happy if I got 300ml per minute from each float bowl drain with one tap open and half a tank of fuel.

Good Luck
Peg
i agree with this advice. Retro :smile2:
 

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Discussion Starter #16
Air leak ! Fixed an air leak on the rear of the air filter and added some Seafoam and things have improved 95%. Still think I need a carb clean, timing and valve check but the majority of the prob was def the air leak. Thx to everyone who tried to help

Steven
 

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Hi Theepic, I wonder if you might want to raise needles a notch?? That's a guess, but don't guess. Study this carb tuning sheet. Mark your grip in 1/8s. Like a ruler long & short lines so you can see at a glance where throttle is. It is the only way to see what part of carb needs changing to effect the part of carb that may not be correct.

Measure fuel flow from each tap. Remove gas cap. It should not speed up flow. If it does, the cap vent may be partly clogged. Remove carb drain & measure fuel flow from blows. The taps should provide way more fuel than can flow through carbs. Way more.

Link looks odd, but it is correct. Print this & put in pocket. Study the guide. Rode test refer to guide & see what it suggests.

https://www.princeton.edu/ssp/65-cub-data/library/amalbritbike.pdf

Too low of float level can effect tickling also. What type carbs do you have? Old version concentric, new non premier, or new premier? The float level is different on new version carbs. Tall new version ticklers can be installed on old original bodies so that doesn't mean anything.

The original carbs would have been 930. Air filters can effect carbs as well. I've found the original fabric gauze which are still sold to work better than the paper elements such as Emgo type. I find it hard to get correct mixture at all speeds with the paper ones. The original type are washable so in the end they are cheaper & last for years.
Don
 

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Discussion Starter #18
Hey Don
Wasn’t ignoring your post you took the time to write out. I’m going to take it back to the builder for a warranty covered check up and do the watch and learn thing this time. Have you ever tried the K&N pancake filters by chance. Hanks again for the info and I did save it
Steven
 

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Discussion Starter #19
Follow up to my lag issue after returning to Mecca (Collins Cycle, Sutersville PA.)

Adj valves
Adj timing
Clean-Adj carbs
Fix air leak
Retorque heads
Adj clutch
Change all fluids
Plugs
Air filters
Pair of K70’s

All good in the hood now. Did a little 82mile test drive and the only issue was the heat. 87degs and city driving two up... not ideal. And think I need to check routing of throttle cables. Other than that all everyone happy

Oh and tacos, tacos makes everybody happy. If not you need to get out more or maybe add in a margarita.
 

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Discussion Starter #20
Well throttle cables were definitely bound up so pulled the tank and moved stuff around a bit to fix that. Primary leaking like a sieve, broke another exhaust bracket so another order from CBS and I’ll get that fixed. Took that opportunity to buy a pozi screw set also so that I can start replacing all of them new and correct. Was a bit hodge podged with hexs and pozis.
 
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