E: Engine Bafflement

[greg brillus]

Only issue I've seen with bikes started on full throttle, is the thing revs very aggressively once it starts, not ideal for a stone cold engine. If your engine starts this way, i'd suggest try not using the tickler and/or the choke.........It appears that just turning on the fuel and closing the chokes, cycle the engine over 2 or 3 compressions with the decomp lever, then kicking seems to give good results. Of course this is pendant on your float levels being ok and all else being ok as well......As far as buying expensive items to cure hard starting, well you can only use what is available now really.......New Amal side bowl carby's have certainly grown to ridiculous prices now.......as for ignition, well finding good re-builders of magnetos is only going to get harder (and who's to say they are any good anyway.......a lot aren't).......a new Tri-spark ignition system is pretty cheap in reality, although it is a coil ignition set up........As many have found out the hard way......do not use an electric starter as a tuning tool to fix your bikes poor running issues.......Once you have an electric starter you never look back........You can ride your bike longer and it will be much easier to sell to a future buyer........Cheers.

 

[BigEd]

The fact that both cylinders fire at the same time suggests the issue lies with one component. Any ideas gratefully received.

You say you have a BT-H magneto. Whether it is an original old BT-H or the later electronic BT-H the cylinders should not be firing at the same time. What type of Amal carburettor? Monobloc, Concentric, etc.

 

[moto8500]

Thank you for all the helpful replies, especially Greg with the warning about the electric starter and Treunvandriel good for you ditching the e bike for the trusted thigh and legs.

I can now tell that I am flooding the engine what with the trickling and choke and Greg's observation that a strong tick over when cold suggests the engine is running rich appears spot on as the plugs are not a nice greyish brown at the electrode but black.

so the question is what to do- adjust pilot screw, rejet again or raise the throttle needle a notch?

I know it is a question of trial and error to get the carbs set up correctly. They are a couple of pre monobloc 276/289 series.

 

[Chris Launders]

You say you have a BT-H magneto. Whether it is an original old BT-H or the later electronic BT-H the cylinders should not be firing at the same time. What type of Amal carburettor? Monobloc, Concentric, etc.

I think he means it starts on both cylinders at the same time, rather than one firing first and then the other kicking in after.

 

[moto8500]

Correct re engine firing. It's a electronic BTH mag.

 

[greg brillus]

Although the 276/289 carbs look similar the 289 is actually much bigger than its smaller brother.......the airflow characteristics through both types is quite different.......Pilot mixture screws (the horizontal one, closer to the manifold) is an air screw, so winding this screw out further will lean off the mixture, inward will make it more on the rich side.......Normal starting point for tuning is to set the screw 1 1/4 turns out from fully seated......I would start by winding each in one at a time and note the exact amount of turns it takes to seat the screw........So long as the carbs are a good snug fit on each manifold, not loose and sloppy once the clamping screw is backed off........with the bike on its center or rear stand (bike upright) stand behind the bike and check that the rear carby is level and square to the engine (bowl vertical and not tilted to the left or right) do the same for the front carby standing in front of the bike looking rearward........the float levels will affect the running, and noticeably at lower engine speed......So a quick check will give a good starting point.........No good trying to lean off a rich running cylinder if the float level is too high.....The pilot jets in the jet blocks of the larger 229/289 carbs do need to be opened up but not too much........20 thou is ideal, 22 or more will be too rich. We will need more info before much more help can be given at this stage........

 

[moto8500]

Thank you Greg for the checks I need to do. When the carbs are trickled so the float chamber is full they continue to fill and leak until the engine starts so do I assume the float levels are too high?

The other question concerns the measurement of the pilot jets in the jet blocks - how is the measurement taken?

 

[greg brillus]

No tickling required before this check.........just a simple visual alignment of the carb/bowl front and rear.........The pilot jet can only be checked with the lower body cap nut (large one at the base) removed and the brass jet block removed........Carry out the mixture screw adjustments first.......plus the bowl alignment checks.

 

[Robert Watson]

What spark plugs are you using. I found my Rapide with the BT-H was herd to start from cold with NGK 7 plugs (cold) and did exactly as you describe; it was a much better starter with NGK 6 plugs

 

[LoneStar]

I think that was probably coincidence, or defective NGK 7 plugs. The difference between heat ranges is in the ease of conducting combustion heat from the center electrode to the plug shell - heat range has no relevance when plugs are cold during startup. Of course after running a while, if the 7 plug was too cold it could become fouled and make for hard starting.