My MK3 does not rev beyond 4500rpm

Boyer uses a cheap dual output coil they sell at a high markup. I use the same spec dual output dual tower coil Matt at cNw sells with a TriSpark. It does not give me any problems (yet), but the cheap dual coils gave me misfiring problems in the past. The old oil filled coils always worked with the Boyer, but I had a 12V setup then. I removed them to make space for over carburetion.

Good luck.
 
Something not mentioned and rare that will kill the top end is a breather set up that suddenly becomes non-functional. Although I'm not sure you could get to 4500 RPM with a crankcase full of pressure. You would definitely blow a seal somewhere eventually if it were the case. Learned this the hard way when I installed a 2S cam that did not have the machine work to support the timed breather in a P11 engine. Took me a few rides to figure out what was wrong. Yes it was dumb, but I wasn't born an expert. That came later after hundreds of dumb mistakes. 🤣
 
Get your spark and timing right first .and If it persists, Weak valve springs as well , did you check seat pressure and full lift pressure,
 
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I use a double-ended coil from a Honda with my Boyer - there are fewer electrical connections. If the motor will not rev because of an electrical problem, you should hear the motor missing. If it will not rev due to timing or jetting being wrong, you should already have checked those. Have you changed the spark plugs yet ?
 
A dual output coil like a Revtek or Accel for a Harley are well proven and mine has lasted well over 20 years. The only issue may be that some have short towers which will arc over in damp weather if the boots aren't siliconed up. These will easily fire a .035" plug gap or spark 1-1/2" to find a ground or the primary terminals if you let it.
Russ
 
batrider said:
A dual output coil like a Revtek or Accel for a Harley are well proven and mine has lasted well over 20 years. The only issue may be that some have short towers which will arc over in damp weather if the boots aren't siliconed up. These will easily fire a .035" plug gap or spark 1-1/2" to find a ground or the primary terminals if you let it.
Russ
Click to expand...
Mine is a Harley Compufire dual coil 3 ohm 45K volts. Better than a cheap dual coil or a K2F hands down.
 
Even if the motor has stuffed valves or rings, it should still rev. If the motor is not missing, the problem is probably flooding. Low crank balance factor can stop a motor from revving high.
 
Well, whatever can only be spark, fuel or timing if valves are set right and motor has good compression, and a bad coil just got to go through till you find the problem, even a broken/short wire, find and fix/replace, just got to go through one thing at a time, have lost a few coils in my time, they do go bad same as plugs.
 
I received two new Lucas 6V coils with new HT leads and spark plugs. I already install them on the bike replacing the faulty Boyer double coil.
Can anybody tell me how do I have to wire them together with the Boyer control box for negative earth?
Some wiring drawing would be welcome.
 
Here you go
 

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Start the motor and turn the throttle - it might be a very simple problem, such as a flat tyre - or a bad hearing-aid or a weak wrist ?
An Interstate insurrection ?
 
Is the intake cam too advanced ? , I had a friend once and he had a rag in the intake port , that motor didn't run too well ! .
 
Shelby-Right said:
Is the intake cam too advanced ? , I had a friend once and he had a rag in the intake port , that motor didn't run too well ! .
Click to expand...
Seen that happen more than once.

Many times more than once actually at race meetings when things get hectic and people "help". 😤😤😤😤😤
 
Following the wiring scheme you kindly provide me it was quick and easy to connect the Lucas coils. The bike started up easily, I checked the timing with the strobe light and Bingo! Now both cylinders produce a strong and continous light at any revs. I adjusted carburation again with vacometer and I had to adjust a bit the Left cylinder that was a bit to accelerated. I get a perfect idle and an engine now seem to me more eager to rev at a maximum of 6000 rpm which was promising.
I made a 100 kms road test:
From idle up to 4000rpm it maybe has a bit more torque, just a little more allowing to use third gear a bit more and not having to downshift to second so much.
I was able to rev up to 5000rpm but no more and is clear to me the engine feels comfortable from 2000 to 4500rpm but it does not feel right beyond.

So the result is I got a bit more revs but still this engine does not want to rev more.

To summarize my engine has:

New piston rings, new head gaskets, head revised with new valve seals, PVC engine breather valve
Cam chain timing perfectly revised
New Amal 923 carbs with:
MAIN JET 220
THROTTLE SLIDE CUTAWAY 3 1/2"
NEEDLE JET 106
REMOVABLE PILOT JET 19

New unbalanced exhaust pipes, open non original Peashooter silencers, K&N air filter directly mounted on the carbs with no filter box.
New triple primary chain with new hydraulic tensioner, piston and spring, new clutch, completely revised gear box that works suitely, 22T secondary engine sprocket (too large for me producing a lazy engine on the twisties).

At this point I can only suspect a crankcase eventually unbalanced or camchaft lobes wear. Or maybe try to dismount the fresh new carbs and see it there is anything wrong or maybe trying bigger main and pilot jets...

The engine starts up cold at first kick and runs perfecty but it is hard to start up warm, it takes me 4 to 5 kicks.
 
javifoto70 said:
Following the wiring scheme you kindly provide me it was quick and easy to connect the Lucas coils. The bike started up easily, I checked the timing with the strobe light and Bingo! Now both cylinders produce a strong and continous light at any revs. I adjusted carburation again with vacometer and I had to adjust a bit the Left cylinder that was a bit to accelerated. I get a perfect idle and an engine now seem to me more eager to rev at a maximum of 6000 rpm which was promising.
I made a 100 kms road test:
From idle up to 4000rpm it maybe has a bit more torque, just a little more allowing to use third gear a bit more and not having to downshift to second so much.
I was able to rev up to 5000rpm but no more and is clear to me the engine feels comfortable from 2000 to 4500rpm but it does not feel right beyond.

So the result is I got a bit more revs but still this engine does not want to rev more.

To summarize my engine has:

New piston rings, new head gaskets, head revised with new valve seals, PVC engine breather valve
Cam chain timing perfectly revised
New Amal 923 carbs with:
MAIN JET 220
THROTTLE SLIDE CUTAWAY 3 1/2"
NEEDLE JET 106
REMOVABLE PILOT JET 19

New unbalanced exhaust pipes, open non original Peashooter silencers, K&N air filter directly mounted on the carbs with no filter box.
New triple primary chain with new hydraulic tensioner, piston and spring, new clutch, completely revised gear box that works suitely, 22T secondary engine sprocket (too large for me producing a lazy engine on the twisties).

At this point I can only suspect a crankcase eventually unbalanced or camchaft lobes wear. Or maybe try to dismount the fresh new carbs and see it there is anything wrong or maybe trying bigger main and pilot jets...

The engine starts up cold at first kick and runs perfecty but it is hard to start up warm, it takes me 4 to 5 kicks.
Click to expand...
By ‘a crankcase unbalanced’ I assume you mean ‘crankshaft’ ?

An out of balance crank CAN cause an engine to hit a rev ceiling. But it has to be very much out of balance, ie to the point you would know that it was obviously wrong.

Have you confirmed that both slides are synchronised AND opening fully? And are you certain that you are actually opening them fully when riding?

When you say it won’t rev, do you mean in top gear, or in any gear? A 22t sprocket is pretty big for a stock engine. You can’t just expect it to rip up to 6k in an instant it top gear, it will need revving through the gears.

The bike has been fully restored, so why do you suspect cam lobe wear ??

Pilot jets will have no impact at all on max rpm at WOT.

As already suggested, you must try bigger main jets.

Failing that, perhaps time to remind you about post #5 …
 
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Fast Eddie said:
By ‘a crankcase unbalanced’ I assume you mean ‘crankshaft’ ?

An out of balance crank CAN cause an engine to hit a rev ceiling. But it has to be very much out of balance, ie to the point you would know that it was obviously wrong.

Have you confirmed that both slides are synchronised AND opening fully? And are you certain that you are actually opening them fully when riding?

When you say it won’t rev, do you mean in top gear, or in any gear? A 22t sprocket is pretty big for a stock engine. You can’t just expect it to rip up to 6k in an instant it top gear, it will need revving through the gears.

The bike has been fully restored, so why do you suspect cam lobe wear ??

Pilot jets will have no impact at all on max rpm at WOT.

As already suggested, you must try bigger main jets.

Failing that, perhaps time to remind you about post #5 …
Click to expand...
Oh yes, I mean crankshaft! And agree I am just thinking about possibilities, the engine runs smooth up to 4500rpm so I doubt the crankshaft could be so much unbalanced.
I will double check both carb slieds are fully opening.
I tried to rev on second and third gear with the same result: it does not rev beyond 5000rpm. Although I did not open the throttle fully because the engine has only 500 miles and I yet do not want to force it so much. But i think it should rev at least to 6000rpm easily which is not doing.

The only part of the bike I did not open myself was the crankcase so I do not know how the crankshaft and camshaft are.

I will revise slides opening, carbs and replace the main jets to 260 ones.
 

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