RM80B not running well

[oldDT]

Hi guys,
Been working on restoring a 1977 RM80 for the past 8 months. It's going great, and I took it for it's first ride in a long time the weekend before last. Went well then, but last weekend not so well. It starts on the first or second kick from cold and idles well, but seems to bog down under load. There is a slight hesitation on acceleration as well. If you have a rolling start it will go when the clutch is released, but from a standing start it just stalls unless the revs are really (about 4000 RPM) high.

I pulled the carby and stripped and cleaned and reassembled it. Made no difference.

About the only thing I changed from the first ride was to move the CDI unit from the frame steering head back under the side cover so I could stick a front number plate on. Do you think there may be a lose wire connection somewhere, and would this cause the problem?

Any advice greatly appreciated thanks.

Kel

PS The bike is running a Mikuni carby from an unknown YZ80.

[Doc]

G'day Kel, I assume the need to move the CDI from the steering head means you have a different front end fitted?? I'd be inclined to think maybe the cdi is not grounding properly now it's been moved. Run an earth wire from the CDI mount to somewhere like the top rear engine mount and see if it makes any difference. Either or the carby may need a good blow out..especially the primary circuit..it was runing well you say so it can't too much..Doc

[oldDT]

Hi Doc, Thanks for the reply. I pulled the carby again and stripped it. Did find some fine sand in the float bowl. The tank had a few dings in it when I got the bike. Not too bad but looked ugly. I sand blasted the tank before repairing it and thought I had the cap and tap outlets blocked. Apparently not well enough :-{ I'll try an inline fuel filter and see what happens. Unfortunately when I went to blow the carby out my compressor went bang and the smoke got out. Knocked out the house safety switch. I'll have to wait till I can get time to get to my brothers place to give it a blow out before reassembly. Wont be till after next week now though, as I have 2 grandkids racing in the Australian Dirt Track Championships this weekend at the Gold Coast. Takes precedence over everything.

Also I noticed that the CDI unit has rubber gromets in the mount holes. I assumed they were for insulation? There again I don't think it has the original CDI either, as there is one wire (blue with white stripe) that has been snipped of. Any idea how to clean bullet connectors? I pulled the 2 plug connections apart and the male bullet ends are quite rusty looking. They are easy enough to clean, but how do you get at the inside of the female sockets?

While I had the tank off I thought I'd check the coil as well, and I don't think it would be earthing too well as there is paint on the mount points. I've cleaned them up as well.

You're right about not having the original front end. When I got the bike the forks were (still are) very pitted, so I machined out the bottom tree clamp of a set of pitbike forks and fitted the RM80 stem bolt to them. They are close to the same length, and now that it's done they will be easy to replace when they screw up, and they're as cheap as chips to buy new. Can replace then almost as cheap as putting new seals and dust covers in the original forks. The bike wasn't rebuilt to race so the lack of originality is no big deal, just a bit annoying.

I'll have another crack at it next week and let you know how it goes.

Thanks again

Kel

[Lozza]

I would be with Doc on the pilot circuit being block could even be the air correction holes in the needle jet a bit blocked to.
Just a question, how did you machine the yokes out, faceplate on the lathe, boring head on the mill or ream them out???Smart move with the pit bike forks BTW.

[oldDT]

Hi Lozza,
Thanks for the confirm on the carby. I'll get some carby cleaner this week and give it a good soak. Make sure everything is clear and reassemble with the filter and see how she goes. My brother only lives at Kallangur (10 minutes away) so I'll blow it all out also.

Thanks for the complement on the forks. I used a mill. I also had to bush the axle holes down to 10mm as the pit bike uses a 12mm axle. Then I had to make up new spacers and a longer axle (10mm chrome rod). Then I had to make up a bracket to bolt to the caliper mount and slot into the original brake hub. Bit of fiddling around, but it all works OK.

I think I'll also remove the old bullet connectors and put in some new spade connectors for the CDI.

Thanks again for the help guys.

Kel

[oldDT]

Hi Doc and Lozza,
Quick update. Carby clean and electric connector clean made no difference. Decided to pull the cylinder off as it felt like compression was down a little. The piston is on first oversize, but the guy I bought it off said he'd put in a new piston (says he's a mower mechanic). The bore isn't brilliant and I think I should go to the next oversize as the ring end gap is almost 0.1 over max spec. Also found that the reed stop spec was way off. Supposed to be 7.35 - 7.4 and was actually only 3.5mm.

I was surprised to find I can still get Wiseco piston kits for a 77 model. Wonders never cease :-} I'll get a 1mm over kit and throw it and the barrel over to my son-in-law. He's an engine rebuilder and does rebuilds for my grand kids (among others) race bikes. Does an excellent job too.

Have a bit of time now to do the top rebuild as my grandson who I'm doing the bike for broke his wrist at a practice day at the North Brisbane track last Sunday. He wasn't too bad with it considering he's only 9, but my daughter tells me he cracked at the hospital when the doc told him he'd be in plaster for 4 weeks. Was a tad pissed that he wouldn't be able to ride the last 4 meetings for the year.

Later guys.

Kel

[Doc]

oldDT..the reeds wearn't jammed open were they?..this could also do what you described.
You can still get a genuine Suzuki 1mm over piston 'set' (piston and rings) $78US. Worth trying a dealer first as it's same piston for TS100,DS80,GT185,FR80.

Failing that I have a brand new 1mm over piston and ring set here I'd gladly swap for a rebore and port chamfer on my TM125 barrel..I can supply the piston

The TS/DS/GT and early RM80 pistons run wider rings but the C-X model RM80's used thin rings either pistons can be used so long as the rings match

This is what I have been playing with for the past week. Has only taken 3 years to get to this stage and probably another 12 months to go before it's done..damn hard model to find engine parts for but I have 98% after I picked up a pair of usable wheels for $20 last weekend hopefully it will only owe me around $500 all up when completed.

the second pic is my other little blappers. I've a TM/TS75 also so it seems I have a bit of an underlying affinity towards the extra small bores 

__**__

[oldDT]

Hi Doc, Danny said he'd do your bore and chamfer for you as long as your not in a screaming hurry. Might take him a few weeks to get to it. If you're still interested in the swap I'll work something out with him to cover his work. I know he has a sun room he wants turned into a bedroom 

Nice bikes BTW. I know what you mean about parts. My DT250A is a problem also. Dylan and Katie are on my back to go racing with them at North Bris. It should go OK in the post classics there when I get it done. This will be a first for me, as I just love to go bush and disappear for a few hours. The links are to a photo of the bush pig (my bitsa bike) and the RM80 with the pit bike forks. I've still got to modify the forks a bit.

Later

Kel

http://autos.ph.groups.yahoo.com/group/honda_clone/photos/view/63a9?b=3

http://autos.ph.groups.yahoo.com/group/honda_clone/photos/view/63a9?b=5

[Doc]

Kel 2 weeks or so for the rebore sounds fine by me. I have another bike I can ride if the situation arises in the meantime the piston kit for the TM arrived today and the barrel is on the bench all ready to be bored.

This will be a first for me, as I just love to go bush and disappear for a few hours.

T'was a first for me too earlier this year as I've been known to frequently mutter words very similar to those you wrote in the above quote  Never the less VMX sure is a fun experience and worth trying at least once. I'd like to get back up to Nudgee before the end of the year..1 ride all year is bloody hopeless 

oh and I couldn't get into to see the pics but I'll try again later

[oldDT]

Try these instead of the other links:-{