My MK3 does not rev beyond 4500rpm

javifoto70 said:
Thank you for so many good ideas and thing to look at. I am also thinking there is something wrong inside the engine and/or transmission. I will start checking the transmission again. The cylinders and head are the only two parts of the engine I did not do myself because the previous owner told me it was done. Maybe this ends up dismantling the complete engine to see what has been done. I will see for at this point after more than 300 hours and 6000 pounds expended (not including the 4500 pounds I paid for the bike) I am starting to be really fed up of this very bike.
It is a petty because the handling of the bike is excelent on back roads and its low weight make it a peace of cake to ride it.
My MK3 does not rev beyond 4500rpm
My MK3 does not rev beyond 4500rpm
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That's a BEAUTY!!!
We got to get that thing going so you can properly FLOGG it.....
Can we see a picture of the right side?

Serious questione here, when you rev it, does the kick starter drop?
Another Q, I believe you put the new Premiers on, what carb or carbs did it have before and did it rev out?
One more Q, can you take a picture of your choke lever?
 
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javifoto70 said:
Thank you for so many good ideas and thing to look at. I am also thinking there is something wrong inside the engine and/or transmission. I will start checking the transmission again. The cylinders and head are the only two parts of the engine I did not do myself because the previous owner told me it was done. Maybe this ends up dismantling the complete engine to see what has been done. I will see for at this point after more than 300 hours and 6000 pounds expended (not including the 4500 pounds I paid for the bike) I am starting to be really fed up of this very bike.
It is a petty because the handling of the bike is excelent on back roads and its low weight make it a peace of cake to ride it.
My MK3 does not rev beyond 4500rpm
My MK3 does not rev beyond 4500rpm
Click to expand...
How on gods green earth can someone score such a machine for 4500 pounds? Ive spent 3x that amount on my bike and it looks like its been pulled through a hedge backwards compared to this one.
 
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Tornado said:
How on gods hreen earth can someone score such a machine for 4500 pounds? Ive spent 3x that amount on my bike and it looks like its been pulled through a hedge backwards compared to this one.
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He didn’t score ‘that’ bike for £4500… ‘that’ bike has cost him £10500 and untold hours of hard labour !

Thats why we need to help him get it sorted !!
 
Are those Avon Super Venoms? They are probably older and a lot rarer than some of the members on this site. 🤣

Nice looking ride.
 
Check the petrol tank taps flow enough fuel, there are cheap knockoffs around where the rubber seals swell restricting flow. Also check the petrol tank cap breather works as that again could restrict flow.
 
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Agree with Kommando but also check petrol pipes are the right size I once had a tee piece wrong bore size and it didn’t flow enough fuel and watch banjo sizes on carb float bowls not all are made the same
 
If the main jets are not big enough or there is an electrical problem - that can stop the motor from revving high, but you would hear it missing. When the motor is revved and has no load, it should spin to at least 6000 RPM. The low crankshaft balance factor and heavy crank create poor throttle response, but the motor should still rev out. It would just vibrate more at high revs.
 
Do we know what version Boyer? If a digital, could it be getting RF feedback from unsupressed HT caps/plugs? Are there Boyers with settable rev limiters?
 
Tornado said:
Do we know what version Boyer? If a digital, could it be getting RF feedback from unsupressed HT caps/plugs? Are there Boyers with settable rev limiters?
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There is a separate box The Boyer rev limiter, with a "screw' to aduster the cut out revs. IT looks like the standard "black box" in size
 

Boyer Rev-Limiter Adjustable for Rd.&Racing | BRITISH Only Austria Fahrzeughandel GmbH

www.vintage-motorcycle.com www.vintage-motorcycle.com

I'm not saying he has a rev limiter, I'm saying something is acting like a rev limiter, If it always cuts out when warmed up at a certain RPM.

When I time a bike to a 5000 RPM ,I barely have the throttle twisted up much. It is no where close to wide open.

But it is true, different Boyers have different needs and coils too, So Knowing the type of Boyer is important , The Micro- power kits have a special coil.
 
Probably a silly question (or I missed in over 100 posts) - what are the letters/numbers on the bottom of the face of the tach? In other words, is there a chance the tach is wrong?
 
marshg246 said:
Probably a silly question (or I missed in over 100 posts) - what are the letters/numbers on the bottom of the face of the tach? In other words, is there a chance the tach is wrong?
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" Sometimes you have to think out of the box, So you don't box yourself in".

Nothing is silly at this point, BUT it could be a silly solution to fix it.
 
Over on another current thread about exhaist popping, it was stated to check the trispark air gap btwn stator and rotor...spec is 2mm and the kit instructions call this out and provide a bit of plastic as a spacer to get it correct. Mentions high rpm issues if out of spec.
Wondering if this bike's Boyer setup needs something similar set correctly?
 
I gave up on the Boyer (mk 1) in my Commando, because it was always trying to break my leg when starting it, refitting the original contact breaker unit which always worked perfectly. The Boyer went on my 88 race motor (no kickstarter).
If electronic ignition units are suspect above mid-revs speeds then they deserve to be dispatched over the hedge.
 
When my 500 barrels were resleeved, bored and honed for new standard size pistons they were left under size with not enough piston clearance. They seemed a little too tight a fit to me so I bought an old bore gauge off eBay and checked it. Took the barrels back and got them sorted. Maybe something similar has happened here?
 
"The fact is that the engine does not rev over 4500rpm on not any gear, it vibrates and does not want to rev."

There is virtually no load on an ignition system or fuel flow with bike in neutral/revving the throttle. If it won't go past 4500 RPM in neutral, as noted and then "vibrates," it sure sounds like a rev limiter since they usually function by cutting the ignition out/in as the revs hit the limiter, drop, rise, hit the limiter again, etc. Due to over-enthusiasm (or poor operational capability) I'm a regular "rev limiter hitter" on several bikes so I'm quite familiar with the way they feel! I'm REALLY good at hitting the 7200 RPM limiter on my Moto Guzzi V7 850! :rolleyes: So there is NO actual rev limiter in your aftermarket ignition system?

IF it revs to the red zone when in neutral, the above does not apply.
 
Carburetion, ignition, or getting ready to seize up are definitely strong runners in the message box guessing game.

When I read posts like this I often wonder if it is a jest to test the expertise of the membership. lol

Anywho, I've had similar happen, but I was not using Amal carburetion, so my cure would be way off.

Has getting pressure out of the crankcase been mentioned? If pressure is building and not evacuated it will act like trying to pull the Queen Marry on dry land with a Vespa.
 

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