'77 LeMans Carb advice

[earemike]

My 'other' '77 850 LeMans has finally arrived and is now registered.

It was running well when I took if for inspections but for the first main test ride I think I flooded the right cylinder on start up and it was only running on one. Cleaning the plug got the bike going again but about 100km later it started missing & then ran on one cylinder. Riding further (to get to a workshop) the issue cleared itself after several km of mainly downhill.

1. I may have had some bad fuel &/or in the 3-4 months the bike has sat there may be water in the bowls of crud in the system (I'm obviously no expert).

If the bike misfires intermittently is fuel contamination a likely cause? I'll be running a bit of metho in the next lot of fuel & go to a trusted petrol station.

At the workshop I replaced the plugs and noticed the left looked cruddy, the mechanic suggested at some stage it has gotten to hot. It also looked a little oily. Given the motor top end (cylinders/pistons/heads) was rebuilt 5000miles ago (& 9 years) I wanted to ask if a little oil consumption is expected, my V11 took about 20,000 km to loosen up but as this bike is new to me I'd like to hear what the experts think. Obviously as I get some miles on it I can monitor this but for now it's an unknown.

Once I've eliminated bad fuel I was thinking about taking the bike to a local tuner but this immediately got me thinking about the carbs. The bike was apparently John Hoffman's and ran 40mm carbs with the B10 cam etc. During the top end rebuild the previous owner fitted 36mm carbs, electronic ignition and lowered the gearing.

2. My question is what carbs would be most appropriate for sporty riding through the hills? I understand this is a "how long is a piece of string question" but I figure John knew his stuff and would have had the bike nicely set up. If I go bigger I'll need to find some cabs so I'm open to opinions on carbs other than dellortos too.

Apologies for such a broad question, the bike generally rides smooth and will rev out but doesn't feel like it really wants to go. Because it's new to me it could be the last owner tuned it for midrange cruizing or it's just a fresh motor that needs time to loosen up. Of course if my plug issue isn't due to bad fuel the carbs might be out and I'll be visiting the tuner anyway.

[NCAmother]

Keihin FCR's are pretty awesome.

[flangeman_70]

Check the choke for sticking on the offending side .

  Dusty

Dusty's on the money.
I would suggest you pull both choke/enrichment plungers and check the bottom seals and clean/lube the bores with some WD40. Then on re-assembly ensure they are seating correctly without the cables, then fit the springs and cables and ensure that there is enough length for them to seat correctly when they are not in use.

Adam

[Charles in Lake Charles]

Check the ignition. If it's a Dyna, they have been known to be defective on one cylinder.

[PeteS]

I have had a Marelli coil go on my '76 so check the coils and all the connections to them. If the rubber tips on the enrichener plungers have a deep circle groove in them you can carefully pry the rubber disk out from the edge and flip it over.  Also Make sure there is slack in the cables.

Pete

[Guzler]

My 'other' '77 850 LeMans has finally arrived and is now registered.

It was running well when I took if for inspections but for the first main test ride I think I flooded the right cylinder on start up and it was only running on one. Cleaning the plug got the bike going again but about 100km later it started missing & then ran on one cylinder. Riding further (to get to a workshop) the issue cleared itself after several km of mainly downhill.

1. I may have had some bad fuel &/or in the 3-4 months the bike has sat there may be water in the bowls of crud in the system (I'm obviously no expert).

If the bike misfires intermittently is fuel contamination a likely cause? I'll be running a bit of metho in the next lot of fuel & go to a trusted petrol station.

At the workshop I replaced the plugs and noticed the left looked cruddy, the mechanic suggested at some stage it has gotten to hot. It also looked a little oily. Given the motor top end (cylinders/pistons/heads) was rebuilt 5000miles ago (& 9 years) I wanted to ask if a little oil consumption is expected, my V11 took about 20,000 km to loosen up but as this bike is new to me I'd like to hear what the experts think. Obviously as I get some miles on it I can monitor this but for now it's an unknown.

Once I've eliminated bad fuel I was thinking about taking the bike to a local tuner but this immediately got me thinking about the carbs. The bike was apparently John Hoffman's and ran 40mm carbs with the B10 cam etc. During the top end rebuild the previous owner fitted 36mm carbs, electronic ignition and lowered the gearing.

2. My question is what carbs would be most appropriate for sporty riding through the hills? I understand this is a "how long is a piece of string question" but I figure John knew his stuff and would have had the bike nicely set up. If I go bigger I'll need to find some cabs so I'm open to opinions on carbs other than dellortos too.

Apologies for such a broad question, the bike generally rides smooth and will rev out but doesn't feel like it really wants to go. Because it's new to me it could be the last owner tuned it for midrange cruizing or it's just a fresh motor that needs time to loosen up. Of course if my plug issue isn't due to bad fuel the carbs might be out and I'll be visiting the tuner anyway.

Nope
It was designed from the start to RUN.
Hitachi square slides are the most mentioned.
The Dellortos do the same job just as well.
Fix what you got.

[rodekyll]

My experience has been that doing something like a non-spec carb transplant has the most chance for success if the bike is already running well.  If you're changing to an unknown quantity because you've got an unknown problem you're introducing cats into a squirrel pit.  I'd suggest solving your problem first and then moving forward.

I just lost three weeks on a project going back over the stuff I'd modified on a project assuming the baseline was good and the problem had to do with my screwing around.  After meticulously inspecting all my work I found that everything I invented was behaving.  The problem was a freak failure of an oem o-ring in an oem part.  I thought I had a solid baseline going in to the mod, but the engine that drove itself to the shop had been on a shelf for two years and the o-ring perished.  I should have tested everything as I was putting it together instead of assuming anything was right.

[earemike]

Thanks all for the guidance.

Yes I should make sure it's running well before I introduce more problems. Bugger me (not literally) but it's really a new engine set up. (cats in a squirrel pit  )

Thanks Charles for the tip not to exclude the Dyna, later I need to learn how to confirm the timing (it's been 30 years & I had an expert near).

Thanks Adam for walking me through checking the enrichment plungers (not saying choke will take some getting used to, especially with my other 850 having a tab labelled 'choke').

Cheers, I appreciate you keeping me on the straight and narrow after letting me spit it all out.

[earemike]

Update:

I got some trusted fuel and had run a bit of metho through to get things back on track. I then checked the enrichment plunger (the seal didn't look that bad, I'm learning!) and decided to do the valve clearances etc as it was on my to do list. While there, since the motor has 5k miles I thought it worth checking the head torque.

I'm not sure if backing the head nuts off and torquing them always results in further rotation but it seemed to me the two RHS exhaust rocker bolts took more torque while all LHS rocker bolts took more torque. I used 30ft/lbs.

Before torquing I also checked the valve clearances & the exhaust were 4 thou or tighter. I'm guessing this contributed to the feeling that the bike didn't rev eagerly. I've gone for 6/8thou now.

With that done I changed the engine/gearbox/diff fluids & my diff sump might be the subject of another thread.

After a couple of short test rides I took it our for a longer run, stopping after 70km. I left the fuel taps on for the short stop & wouldn't you know it the bike started urinating on itself. Looks like I'm checking that carb float soon...

Headed for home the bike died (electrical) & I had no idea. At least it was a sunny winters afternoon! After a few hours on the side of the road I shorted the kill switch (in case that was the issue) and noticed the plugs were looking good (one good thing!). Knowing I could get a tow in 3 hours I took the time to fiddle with every wire I could find to check the connections, an electrician even stopped & checked that my fuses (which looked ok) were good. Before leaving me with a roll of tape.

Eventually the wire from the distributor to the dyna ignition fell off in my hand, looks like the wire they use is a bit average & the vibrations were enough to break it. I doubt this contributed to the running on one issue but at least I've found the source of another problem. I bodged it by hand & with 4 stops on the way home using the tape supplied I made it. Pain in the backside but a small win for persistence!

I'm hoping bad fuel and poor valve clearances contributed to the fouling but the amount of soot coming out at warm up means I'm still thinking of getting the bike to a carb tuner. Although that won't happen until I fix my carb leak. Incidentally the previous owner got back to me & mentioned there could be deteriorated rubber in the carbs "like the float bowl drain"  which he replaced. I'll have to look into it but it also means the previous owner may have fiddled the tune.

Thanks for the guidance to date, I'll have this LeMans running smooth soonish!