Rev 3 270 4 Stroking ?

[on_one_wheel]

HI

I am working on a 2001 rev 3 270 that a mate has just bought, the bike has been neglected somewhat and ime trying to clean it up and get it running as it should. Its biggest problem is that its 4 stroking, from halv revs and wont rev out far.

So far ive fliped the reeds over to get them sealing again, cleaned the carb, reset the float height wich was out by a long shot ( low ) as per owners manual but its far from running perfect.

Mikuni 26 / 683

145 main jet

5c23 needle

3rd clip

1 1/2 to 2 1/4 air bleed

1 1/2 idle mix screw

what ime looking for is atleast someone ho knows the base carb settings including the idle mix screw,

also some advice on what the problem is likley to be.

All susgestions will be welcomed.

Thankyou.

Edited March 16, 2010 by on_one_wheel

[kasob1964]

Hi,

I have a 2002 250cc Beta Rev 3 with similiar running problems. Stator and CDI faults have the same resulting missfire when broken. I have just recieved parts from Lampkins to try. I'll let you know what happens!

[feetupfun]

I have seen this problem in my friends 2001 Rev 3 and his problem was piston ring blow-by. Fixed with new rings.

Hard to diagnose yours via forum postings though - yours may be stator failure. The stator problem can cause an effect very much like rich mixture above a certain RPM because the ignition cuts above a certain RPM, causing misfire.

Standard carby settings are fine. Most people go through hours of changing things on the carby, only to find that it was not the problem.

There was a good reason the float height was set low and you will find out why when you ride the bike more. Set the idle mixture screw to suit your bike. The standard setting or anyone elses setting is only a guide.

You didn't list the pilot jet size and that is the thing that people commonly change.

[on_one_wheel]

I have seen this problem in my friends 2001 Rev 3 and his problem was piston ring blow-by. Fixed with new rings.

Hard to diagnose yours via forum postings though - yours may be stator failure. The stator problem can cause an effect very much like rich mixture above a certain RPM because the ignition cuts above a certain RPM, causing misfire.

Standard carby settings are fine. Most people go through hours of changing things on the carby, only to find that it was not the problem.

There was a good reason the float height was set low and you will find out why when you ride the bike more. Set the idle mixture screw to suit your bike. The standard setting or anyone elses setting is only a guide.

You didn't list the pilot jet size and that is the thing that people commonly change.

Was the float set high to stop it from overflowing when on steep angles?

also ile post the pilot jet size when i get back to the shed.

Cheers

[feetupfun]

Yes the Rev 3 carby is leaned forwards lots and a front down attitude makes it worse. If you do a search on the Beta Forum you should find hundreds of postings on this issue with many suggestions for how to avoid losing petrol out the overflows. It might even be a pinned topic.

What is "1 1/2 to 2 1/4 air bleed"?

[on_one_wheel]

Yes the Rev 3 carby is leaned forwards lots and a front down attitude makes it worse. If you do a search on the Beta Forum you should find hundreds of postings on this issue with many suggestions for how to avoid losing petrol out the overflows. It might even be a pinned topic.

What is "1 1/2 to 2 1/4 air bleed"?

By that I mean the air adjustment for the pilot circut.

[kasob1964]

Hi,

I have a 2002 250cc Beta Rev 3 with similiar running problems. Stator and CDI faults have the same resulting missfire when broken. I have just recieved parts from Lampkins to try. I'll let you know what happens!

Hi Again,

Fitted carb last night after cleaning and adjusting the float level. I thought that I'd start it up and check how it's running before I fit the new stator and CDI. Shocking! It now runs perefectly. It pulls like a train in high gears.

Running symptoms were pinking/detonating/4 stroking/missfire when under load. It sounded horrible and would not pull cleanly. It was worst in higher gears. A 125cc would pull away from me on a grassy field! If you tried to pull 3rd, 4th gear it would smell hot and the fan would take ages to cool the bike down.

I'm going to keep the electrical bits for a week and trial the bike this weekend just to see if the corrected bike is a temporary thing? I've been chasing this around for 8 months!

The only changes to the bike from the last time it ran poorely are;

-Set float level almost horizontal. I left it slightly elevated. It was 15 degrees elevated. Was the engine starved of fuel?

-Completely disassembled the carb and used air to blow out all passages.

-I have run a petrol that had a little bio fuel in it. This bio additive can become thick like jell with time. Was this blocking jets?

-While i was fitting the carb to the bike I noticed that the head side jubilee clip was not sitting at the same angle with the carb. It took a little careful effort to make sure it was parallel to the carb face. Was this introducing an air leak?

I should try to reintroduce the problem but I think I'll compete this weekend to try and get some enjoyment out of it first.

Good luck!

[on_one_wheel]

Thats great news Kaosb1964 !

All the things you have mentioned are pointing to a lean mix as you say.

I am of the belief that carburettor manufactures set a spesific float level for a very good reson, and any changes to it will affect its performance.

Ethanol is a great fuel and has some good points but it has two main drawbacks, firstly you need more of it to make the same bang and secondly it absorbs water from the air readily causing gelling with some premixes and promoting oxidation. By adding bio blended fuels without jetting changes you are effectively leaning the mix a little. Personaly I only run 98 octane or higher fuel in anything that I want to perform.

I too have noticed a marked inprovment in the engines problems after the carby work ie. it revs heaps harder.

I am waiting untill I get some new parts before I try to tune it any further, such as a new air filter to replace the torn one, new inlet manifold to replace the perrished split and possibly leaking one, some reeds to be sure to be sure and lastly a throttle cable to replace the worn out prickley and kinked cable that is on it. The next check will be the ignition timing.

All the obvious problems with the rev 3 i am working on are pointing to a lean mix like yours.

Ile know in a day or two if ive fixed it.

Keep ya posted.

Edited March 17, 2010 by on_one_wheel

[on_one_wheel]

Ime pleased to announce that the rev 3 is now fixed !

After much stuffing around fixing little things, none of which sorted out the four stroking problems, we fitted a new stator and BINGO ! she reves out like a champion. Its now running sweet and will only get better with some fine tuning. I have now been told that rev 3's are prone to such problems.

I think it cost around $300 aust. and worth every cent of it. Time to go riding

Edited March 29, 2010 by on_one_wheel