I have eventually managed to get my motor done on my MC18SP, popped it in, connected everything and started her up. It started on the second kick. Now that I have put a couple of km's on it, there is a little problem that is irritating me. When I start it up from cold, with no choke at all, it would start first kick, but it would idle at about 4000rpm for about a minute and then settles down to normal levels (+/- 1300rpm). If I pull the choke in this minute or so of high idling, the revs/idle actually drop to normal levels as well. My first thought was that this means that the air screw settings are incorrect, I had it set up initially as per the diagram in the workshop section on this site, 2 and 1/8 turns out on bog standard jetting and pipes... I have tested every 1/8 increment from 1.5 turns all the way up to 3.5 turns. Same result. I have re-cleaned the carbs checking that all jets and jet sizes are within spec, checked that all the air channels in the carbs are open and clean, checked all my air correction piping, the air correction solenoids, inlet rubbers, expansion tanks etc for leaks and correct operation, all fine. RC-Valves are set up correctly and working properly, TPS tests fine on multimeter.

When the engine is warmed up it runs well, idles fine and runs strong all the way to about 11000rpm and then slightly wanes off on its way to 12000rpm. Its just this high idling on cold starup issue, any ideas anyone?

Jacques.


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I don't have a clue what is causing this problem, but,..
Possibly?, there is a very slight leak in one of the needle valves that fills the float bowls when the bike sits for a while and this would give a rich mixture when starting from cold that would make the bike start easily with no choke and idle high until enough fuel is used to get the float levels back to normal?

Or,... maybe it is a fault with the air solenoids, but I'm really just making that up out of pure stupidity.
My 2 cents anyway.

Good to see you have it up and running already for summer. Well done.

I have same exact problem, idles high cold, no choke, then comes down.

Noticed oil leak from crank seal so it's coming apart now, suspect that may be an air leak causing it

Dmitry wrote:I have same exact problem, idles high cold, no choke, then comes down.

Noticed oil leak from crank seal so it's coming apart now, suspect that may be an air leak causing it

Hi Dmitry,

I seriously doubt if mine could be the same problem, I totally rebuilt my engine, new (genuine Honda) seals all round, no leaks to be seen anywhere. The only seal I did not replace was the centre bearing inner seal on the crank, did replace the thin rubber one on the outside of the bearing casing. I did however check the centre inner seal when I was building my motor using very primative means, when I had the two casings together I poured some petrol in the one crank case and checked if it maybe leaked through into the other... tested fine.
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I love the smell of two-stroke in the mornings!

TuckerBag wrote:I don't have a clue what is causing this problem, but,..
Possibly?, there is a very slight leak in one of the needle valves that fills the float bowls when the bike sits for a while and this would give a rich mixture when starting from cold that would make the bike start easily with no choke and idle high until enough fuel is used to get the float levels back to normal?

Or,... maybe it is a fault with the air solenoids, but I'm really just making that up out of pure stupidity.
My 2 cents anyway.

Good to see you have it up and running already for summer. Well done.

Hey TuckerBag,

Thanks, I am releived it's finally running, be it with some teething problems. As for the slight leak on the needle valves, dont think so... I have this habit of closing my fuel tap as I am parking the bike, something learned from my early years riding old clunkers with faulty floats or flaot levels. I know my fuel tap works 100%.

Just a quickie question though, the little 'filter' for the air correction, that fits onto the airbox in the front, would that make a difference if that were to be, how would we say, slightly stuffed? I opened mine up, seems a bit soggy inside?!? And obviously causes air to move through it with more effort.
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I love the smell of two-stroke in the mornings!

Urkie wrote:

Dmitry wrote:I have same exact problem, idles high cold, no choke, then comes down.

Noticed oil leak from crank seal so it's coming apart now, suspect that may be an air leak causing it

Hi Dmitry,

I seriously doubt if mine could be the same problem, I totally rebuilt my engine, new (genuine Honda) seals all round, no leaks to be seen anywhere. The only seal I did not replace was the centre bearing inner seal on the crank, did replace the thin rubber one on the outside of the bearing casing. I did however check the centre inner seal when I was building my motor using very primative means, when I had the two casings together I poured some petrol in the one crank case and checked if it maybe leaked through into the other... tested fine.

I'm not saying leaky seals are the real cause since I have not fixed the problem yet, just my suspicion.
My bike is also R5K, perhaps the air solenoids as Tucker suggested?

My r5k has a similar problem, i just let it warm up before riding and lower the idle until it does.i always suspected an leak maybe on the carb rubbers that disappears once the expand with heat.
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