Hi, I'm new here so please go easy on me.

My firend recently rebuilt a MC28 which was a basket case. The barrels were badly damaged but we managed to source a complete MC16 motor. We fitted these barrels and new pistons. On starting all seems fine and revving in neutral is fine. On the road the engine dies (almost stops) the faster you try to go (under load).
The carbs have been rebuilt using genuine parts from Thailand
It has new Tyga exhausts


Any ideas anyone?

Hi and welcome here.
After a rebuilt many times from the to much oil which you put on the parts during the assembling the sparks plugs are gone and need to change them.
So try to change at first your spark plugs and if it doesnt fix check all the electricals from the coils to the wire connections.Your rc valves are working?

Thanks for the quick reply stefanos. Sure its not a plug problem as I've changed them for new ones many times. The RC valves are working fine too.


Just bought the full service manual from this site so I hope this will help trying to locate the problem.


Any further input would be greatly appreciated........please!

How much time this bike was stable in not working condition?
Do a crankshaft leak test to see your seals,especially the center seal.
Your spark plugs when you take them out what colour they have?

MC16 cylinder on a mc28 engine? I think thats the problem there.

Could be slow because it's a 28 ? Not sure using 16 cylinders would be good for power, most people with 16 upgrade to 18 cylinders for more power.
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it wouldn't be fun if it was easy!

It should run ok with '16 cylinder but as the ports etc are very conservative it won't make the same power as a stock de-restricted '28. If the bike is still restricted though I doubt the cylinder will make any difference as they only make 38hp-ish anyway.

If the bike revs freely etc when not being ridden but looses power when being ridden to the point the engine will almost stop then something else is wrong.

Apart from the barrels if the rest of the bike standard? Are the carbs jetted as stock? Has the bike been de-restricted?
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If I have to take the carbs off once more...

A stock '28 on Tyga pipes would probably make a tad over 50 bhp as most of the restriction is in the pipes. The '16 barrels aren't helping and it'll never pull hard at the top on the stock carded PGM-IV but it should run OK and be perfectly rideable, after all the MC16 is.
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Please do not PM me technical questions, if you can't find it on the Forum start a thread

Thanks everyone for your replies. When I mean it doesnt run well when changing up the gears, I mean its like riding a restricted ped! Its interesting that fontyyy says the MC16 barrels should let it run fine. They do look pretty much the same inside.

Can anyone tell me what size jets an MC28 with Tyga pipes should be?

I'm sure its just something daft, its just a matter of fettling.

fontyyy wrote:A stock '28 on Tyga pipes would probably make a tad over 50 bhp as most of the restriction is in the pipes.

10 - 14hp from a set of pipes..... and on an MC28? I seriously doubt it.

If, and it`s a BIG if, it makes 40hp, you`re saying a set of TYGA`s are worth 11 - 12hp; a 30% increase in power.

If it makes the more likely 38 - 39hp like stephenrc45 quotes, to make "a tad over 50 bhp" (worst case to best case) you would need to see an increase from the pipes of around 34%.

It ain`t gonna happen.

MC28 with MC16 barrels and TYGA`s...... more like 40~45hp, if you`re lucky. The TYGA`s will likely be totally inappropriate for MC16 exhaust timing. It should run, and run OK if twiddled with, but it`s never going to go any better than a stock MC28, and probably a bit worse.

Better than spending money on shiny expansion chambers would`ve been to get on Yahoo and buy some MC21 or MC28 barrels.
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Vampire?

Probably because the standard pipes are restricted with washers welded into the top to reduce gas flow??? Removing the restriction in them would release a good few horses. Have you looked inside the pipes?
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it wouldn't be fun if it was easy!

dunkenb wrote:Have you looked inside the pipes?

Yes...... have you looked at a standard PGM4 ignition, MC16 exhaust port timing and compression?!
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There`s no cure for stupidity… but with the endless supply of stupid people around me, I must be close to finding it!

The Lizard tells it like it is!

Read - Learn - Post... not - Post - Learn - Edit!

Vampire?

My completely stock except jha pipes mc28 made over 50bhp, another 4bhp was released with a mc21 flywheel. Fontyy is right in its the standard exhausts that heavily restrict the mc28, yes there is more in the standard card ignition but a lot of it is in the pipes.

The MC28 has new Tyga pipes as stated in my original post so I guess that rules out any "restrictions" in the exhausts. My guess is as NSR-Lizard suggests that the MC16 barrels don't line up properly (ports).

Thanks for all your help so far

Why don't you compare the ports to your 28 barrels and have them the same ? Check your squish and head volume . If it still does not perform then you may have to replate your other barrels and reuse them .