xvivalve wrote: ↑Sun Aug 09, 2020 1:26 am
No need to leave them slackened, just make sure when tightening them they don't cause the bracket to rotate.
I don't see how that bracket can affect either carb when the cable is slack, if there's enough slack between the arms on the linkage spindle and the forks on the carb throttle spindle. That it does suggests to me that one or other arm is tight on the tine of the fork.
Grahan
The 16v Slant 4 engine is more fun than the 3.5 V8, because you mostly drive it on the upslope of the torque curve.
Factory 1977 TR7 Sprint FHC VVC 697S (Now all of, but still needs putting together)
B&Y 73 Dolomite Sprint UVB 274M (kids!)
1970 Maroon 13/60 Herald Convertable (wife's fun car).
It's all about the sequence of assembly Graham; it is the tightening of the bolts that puts a turning motion on the bracket which then puts pressure on one of the forks, so forks that are correctly aligned can be distorted if the linkages are dismantled and reassembled without being aware of this.
I suppose. But setting the position of the arms on the throttle linkage spindle so their pins fit correctly in the forks on the carb butterfly spindle should be about the last job in the process of mounting the carbs - with the possible exception of connecting and setting up the cable so it don't pull with no foot on the pedal and just reaches where the butterflies are horizontal with the pedal fully pressed. So that should account for any load that positioning the linkage mounting plate puts on the input lever on the throttle linkage spindle.
When those arms on the linkage spindle are set, more or less the next job should be setting the main jets at 12 flats below the step.
Graham
The 16v Slant 4 engine is more fun than the 3.5 V8, because you mostly drive it on the upslope of the torque curve.
Factory 1977 TR7 Sprint FHC VVC 697S (Now all of, but still needs putting together)
B&Y 73 Dolomite Sprint UVB 274M (kids!)
1970 Maroon 13/60 Herald Convertable (wife's fun car).
It was in this thread https://forum.triumphdolomite.co.uk/vie ... ms#p329770 that dollyman was suggesting you need to unclamp those arms every time you balance the carbs so you're certain the carbs are set independently, and then set the arms after.
Personally, I think you only need to unclamp and reset those when you've changed the linkage, e.g. the link arm that connects the cam follower to the lever on the throttle spindle - it's exact length affects their positions - or swapped or majorly rebuilt the carbs - the position of the forks on the butterfly spindles changes their setting too. But it must be done late in the process after those sorts of changes, and then needs checking periodically against wear, e.g. in the cam and follower, pins and forks, etc.
Graham
The 16v Slant 4 engine is more fun than the 3.5 V8, because you mostly drive it on the upslope of the torque curve.
Factory 1977 TR7 Sprint FHC VVC 697S (Now all of, but still needs putting together)
B&Y 73 Dolomite Sprint UVB 274M (kids!)
1970 Maroon 13/60 Herald Convertable (wife's fun car).
Granted. But when doing jobs like replacing carb mounts on a running car, for example, not everything is taken apart to component level during disassembly/reassembly.
Yes, but any removal of the carbs or big chunks of linkage still behoves resetting those arms on the throttle link spindle, even though it is a bit of a fiddly a job. And fixing a problem like the link plate mount affecting idle by fiddling with the plate mount is just wrong - treating the symptoms not the disease.
Graham
The 16v Slant 4 engine is more fun than the 3.5 V8, because you mostly drive it on the upslope of the torque curve.
Factory 1977 TR7 Sprint FHC VVC 697S (Now all of, but still needs putting together)
B&Y 73 Dolomite Sprint UVB 274M (kids!)
1970 Maroon 13/60 Herald Convertable (wife's fun car).
Yes, he COULD completely reset everything associated with the linkeages, but when there is nothing wrong with how they are set up, simply that tightening the bolts has caused the bracket to ever so slightly rotate causing a problem, slackening the bolts and allowing the plate to regain its natural position is a very simple fix by comparison; it is undoing the root cause of the problem. A two minute job.
Alternatively, as you suggest, he could accept the new location of the bracket, and set everything up to accord with that position. Potentially, half an hour plus...
It's not like rotating the link plate, either parallel or transverse to the line of the engine, can rotate one end of the throttle spindle to open one carb and not rotate the other. So if only one carb opens, that means that arm is set wrong relative to the other, and the two cylinders it fuels will always be doing more work than the other two, even when the strain the link plate causes is taken off.
Graham
The 16v Slant 4 engine is more fun than the 3.5 V8, because you mostly drive it on the upslope of the torque curve.
Factory 1977 TR7 Sprint FHC VVC 697S (Now all of, but still needs putting together)
B&Y 73 Dolomite Sprint UVB 274M (kids!)
1970 Maroon 13/60 Herald Convertable (wife's fun car).
Understand there is clearly a debate to be had here on the level of work required to get this right, and I can't contribute to that with any authority but I just wanted to again say thanks for everybody's input. I will now tackle the issue armed with a lot more knowledge than I had before. Probably a little while before I can pick up again but will be happy to share my experiences and hopefully get the benefit of this community's experience too.
Setting idle means loosening all. First thing to do is set the mechanism. The arm has to rest in the roll. You adjust this by the throttle cable adjuster. Then you balance/set idle by the idle screws and then you tighten the two arms on the link shaft in a way both carbs start moving exactly the same. The pulling the choke you set the fast idle on both the same.
In your attempt to adjust and tune mixture or ignition timing idle will alter. You have to loosen both arms on the link shaft again, adjust idle, set and tighten the link arms and check choke fast idle again.
This way you have the carbs balanced and a smooth take off.
Sometimes you first have to solve play by wear in the mechanism also.
You have to check full throttle also with the engine off. 7 out of 10 engines I adjust aren't full throttle opening with the pedal on the floor by play or wrongly adjusted.
Jeroen,
According to the ROM sequence for Carburettor Tune and Adjust (19.15.02), you do the mixture (steps 10 to 12) and idle (step 13) and then slacken those arms, set to 1.5mm/60 thou between the square pins and lower tines of the forks on the butterflies and then tighten again (step 14).
I would say that will work if you started from a situation where the arms were already about right enough that the idles will set ok. But if one or both arms are too far advanced (no slack), the idle won't set low enough and there's at least risk their settings will interact. So if you've changed anything that might affect them, like the link plate mounting, etc., you have to at least slacken them before setting the idles. You can set and tighten them then do the idles or leave them and set and tighten after the idles.
The issue in setting those gaps before setting the idles is that you will then be certain that the butterflies will open the same when the engine is running under load. Whereas, doing it after setting the idles means they open by the same angle from where they were at idle for any given pedal movement. And if there's any difference between how far down the two idle screws are set, that difference will always be locked into how far open the butterflies will be.
And my belief is that, when the pedal is fully depressed, both butterflies should be dead on horizontal, not one of them flat and one not quite. It might not be much of a difference, but it might not be none either (neither?)
More importantly, considering what a pain it is to re-tighten those arms without one of the little buggers moving as you do it, if you set the gaps first, with the idle screws out, they shouldn't need touching again, and you can fiddle with the idles to your heart's content - at least until you have the forks off the carb spindles or move the link plate, etc. The cost is a very small extra slack in the pedal, equal to what extra it would need to idle the engine on the pedal with the idle screws fully out. I've never measured what that is, but I don't think it's much.
Graham
The 16v Slant 4 engine is more fun than the 3.5 V8, because you mostly drive it on the upslope of the torque curve.
Factory 1977 TR7 Sprint FHC VVC 697S (Now all of, but still needs putting together)
B&Y 73 Dolomite Sprint UVB 274M (kids!)
1970 Maroon 13/60 Herald Convertable (wife's fun car).
That bit about setting the gaps between the pins and tines before setting the idles means do it with the idle screw fully off the throttle arms with everything slack.
Graham
The 16v Slant 4 engine is more fun than the 3.5 V8, because you mostly drive it on the upslope of the torque curve.
Factory 1977 TR7 Sprint FHC VVC 697S (Now all of, but still needs putting together)
B&Y 73 Dolomite Sprint UVB 274M (kids!)
1970 Maroon 13/60 Herald Convertable (wife's fun car).
And the 1.5mm gap is between roller and progression lever with both arms on the fork tines. So the gaps between the arms and the tines with the roller in the lever will be less, cos the arms are shorter than the progression lever.
Graham
The 16v Slant 4 engine is more fun than the 3.5 V8, because you mostly drive it on the upslope of the torque curve.
Factory 1977 TR7 Sprint FHC VVC 697S (Now all of, but still needs putting together)
B&Y 73 Dolomite Sprint UVB 274M (kids!)
1970 Maroon 13/60 Herald Convertable (wife's fun car).
The book of adjusting carbs is written by a man with a vision and there are more of these visions. Adjusting idle you do with both arms loosened. When the idle and mixture is (finally) correct you set the arms that both carbs start moving/opening from idle at the same time. It isn't neccessary the arms are touching the forks at idle. The only thing is both carbs have to open at the same time.
Setting the arms at both throttle valves open 90 degrees has no use. When the engine idles and you move one throttle valve minimal the engine will hesistate. The most important is when touching the pedal the engine will rev evenly. When the throttle valves aren't at the same angle at idle after balancing and you want to compensate by the arms making one carb opening first and then the second for having the throttle valves opening further at the same angle you will have an uneven unbalanced take off. When under load one valve is 40 degrees open and the other 42 doesn't make any difference and isn't noticable.
Set your idle, then have both carbs opening at the same time gives the most smooth running engine and take off.
I accept that whether you set the arms after the idle so the butterflies move together for small openings, or before so the butterflies are open the same when the engine is under load, is a matter of preference - maximizing smoothness of take-off or maximizing power output; you probably can't have both.
However, the point is still this: You really need to do this job of setting those arms at least after every major overhaul of the carbs or linkage. Not doing that can lead to issues like not being able to get the car to idle slow enough - the arms must not touch the tines of the butterfly forks before the idle screws are at least as far out as they could ever need to be. And adjusting the limit of the idle setting by playing with the linkage plate mounting is the wrong way to address the problem. Whether you do it only then, when you adjust the idle, yearly, monthly, or every time you go for a drive is not the point.
I just think that adjusting those two leavers every time you set the idles would be far more trouble than it could possibly ever be worth, given that the job's a biatch to get right. Hence, I shall stick with doing it only after any significant disassembly of the linkage/carbs, and not fiddle with it just because I've adjusted the idles and or mixture. And since that means I can't set it to maximize smoothness of take off, because that will be modified when I change the relative settings of the idle screws, I might as well set it to maximize power, which is not affected by the idle screws. And doing that also ensures that I can always set the idle, wherever the mixtures are set for whatever reasons, without having to do this really damned anyong job again.
Graham
The 16v Slant 4 engine is more fun than the 3.5 V8, because you mostly drive it on the upslope of the torque curve.
Factory 1977 TR7 Sprint FHC VVC 697S (Now all of, but still needs putting together)
B&Y 73 Dolomite Sprint UVB 274M (kids!)
1970 Maroon 13/60 Herald Convertable (wife's fun car).
