Freshly rebuilt Moby 50V idle issue

Jim Swain Jr /

‘79 50v. Bought it a year and a half ago in pristine shape. Sat in a basement forever unused. Seller got it started right up. Very shortly after I bought it, it ended up seizing the piston. Guessing too lean was the issue. I pulled the engine after that and started to dismantle for a rebuild. Then I moved.....

Finally a year later I dove back in. Replaced everything. All seals. Bearings. Needle bearings. Gaskets. New piston rings with a good used block and matching piston. Original Gurtner carb. Fully disassembled and rebuilt with new guts. All my parts have come from treats. Fully derusted the tank. What a bitch. I have container with 250ml of rust in it. New petcock. Online fuel filter. New belt. New plug. Points adjusted and cleaned. Timing set at 1.7 BTDC.

Took it outside this afternoon. Started right up first try. Was pumped. But it will not idle to save my life. I took it for a 5 mile ride and I have to keep tapping the gas to keep it alive when I’m stopping/stopped. Runs smooth and hits 35 mph downhill ;)

Idle screw makes no difference. I’ve sprayed carb cleaner everywhere while the throttle is held open slightly. No change in rpms at all. Don’t think I have any air leaks anywhere.

Over the course of this engine rebuild I’ve read a ton on mobys and just not sure what the best thing I should try tracing down is at this point. I’m not sure if it’s my carb but like I said I fully stripped and cleaned it out. I suppose an idle passage could be blocked again. Maybe I’ll make that my first thing to pull apart.

Re: Freshly rebuilt Moby 50V idle issue

compression good? are u running the airbox? it holds fuel mist, enrichens fuel mix.

Re: Freshly rebuilt Moby 50V idle issue

Jim Swain Jr /

Airbox is on yes.

Didn’t run a compression test. Just air leak test with soapy water while the engine was in the vice.

Re: Freshly rebuilt Moby 50V idle issue

looking on myrons page, nice visual cutaways, looks like theres an idle hole in your diffuser, might be clogged.

Re: Freshly rebuilt Moby 50V idle issue

Jim Swain Jr /

I’ll be pulling the carb apart again this week. I swore I had everything spotless on that carb. I’m sure I could of missed something.

Can’t wait to get all the trim back on this thing. Its so untouched through the years. It’s a wonderful time capsule.

Re: Freshly rebuilt Moby 50V idle issue

Jim Swain Jr /

Pulled the carb apart again this morning. Double checked the jet and recleaned it out. Cleaned and check the atomizer again and idle hole on it and all the idle passages. Still no luck with the idle.

Re: Freshly rebuilt Moby 50V idle issue

for the air box u got that little box w the screen? hows conpression feel.

Re: Freshly rebuilt Moby 50V idle issue

U might try drill out idle jet with tiny hand drill bits one size at time starting with smallest, if u go too big just solder and redrill

Re: Freshly rebuilt Moby 50V idle issue

Jim Swain Jr /
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Pictures of airbox attaches. Tried it with it on and off.

I haven’t put a huge on for an actual number compression test but it runs fine so I’m guessing compression is decent. I’ll try and get a gauge on it tomorrow.

“Idle jet” is just a teeny tiny hole in the side of the atomizer. Tiniest bit I could find would be a big jump I think.

Re: Freshly rebuilt Moby 50V idle issue

Jim Swain Jr /
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Just pulled the plug for shits and giggles

Re: Freshly rebuilt Moby 50V idle issue

check decomp closing all the way. plug looks rich, is the choke closed off? run a ground to the motor to the frame if ya dont have one.

Re: Freshly rebuilt Moby 50V idle issue

Jim Swain Jr /

Decomp was a good seal when I had the head off. The cables are adjusted properly.

Choke is closed off. It’s one of the annoying bottom pull ones.

I’d rather a slightly rich plug at the moment than lean as the piston seized up right after I bought it.

Re: Freshly rebuilt Moby 50V idle issue

Charles Cole (OFMC) /

Really nice looking bike. Hope you get it dialed in soon.

Re: Freshly rebuilt Moby 50V idle issue

>

> I’d rather a slightly rich plug at the moment than lean as the piston

> seized up right after I bought it.

^^this is probably why it wont idle. too rich, didnt notice u put a bigger jet in or you didnt mention it in your og description. put the og back in, and watch temps with a temp sensor. dont forget to ground the motor.

Re: Freshly rebuilt Moby 50V idle issue

Jim Swain Jr /

Motor is grounded. Original 58 jet in the Gurtner. Nothing upgraded.

Re: Freshly rebuilt Moby 50V idle issue

Re: Freshly rebuilt Moby 50V idle issue

Jim Swain Jr /

Interesting. This thing clearly has had a 58 for most of its life. I’ll have to find a 56. Treats only has a 54 and I have that but I don’t want to run too lean.

Re: Freshly rebuilt Moby 50V idle issue

Jim Swain Jr /
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Took it out for 2 mike ride since it was 50 when I got home just to see how it was after cleaning the carb that second time.

When I got it home it and I let it stall I decided to try and start it again. Couldn’t get the clutch to catch and turn it over. Engine was very hard to turn. Even by hand. But it was still moving. Not seized. didnt have my infrared thermometer handy to check temp. Pulled the plug and put a couple drops of two stroke down it and it’s movinf nice and free again.

Compression gauge is on order.

When I pulled the plug this time it looked a lot different.

Re: Freshly rebuilt Moby 50V idle issue

Jim Swain Jr /

Think it’s time to cut the carb out of the scenario. Should just grab a dellorto 14:12 and be done with it like every other Moby on the road. (edited)

Re: Freshly rebuilt Moby 50V idle issue

Jim Swain Jr /

150 psi on a compression test.

Dellorto 14:12 cane in last night. That’s my next step.

Re: Freshly rebuilt Moby 50V idle issue

Bruce Zapper /

What jet are you using in the Dellorto?

Re: Freshly rebuilt Moby 50V idle issue

Jim Swain Jr /

Haven’t installed it yet. Comes with a 57

Re: Freshly rebuilt Moby 50V idle issue

Jim Swain Jr /

Also I feel like I might have the wrong belts. Every one I’ve tried from treats for this bike (A30) seems to pull to motor in from the spring stop a decent amount. It’s probably pulled in 1/3 from normal resting position. You can sorta see it in the pictures above

Re: Freshly rebuilt Moby 50V idle issue

Bruce Zapper /

I would try the 57 first,I don't think the belt would make a difference,take the belt off and start with a drill.

Re: Freshly rebuilt Moby 50V idle issue

Jim Swain Jr /

On the belt it’s just meaning I don’t get full variation is all.

Better pictures of the motor in default position no belt and with belt.

Started mounting the carb this morning. Need to modify the throttle cable

Bendy a bit tonight

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Re: Freshly rebuilt Moby 50V idle issue

Bruce Zapper /

Did you a a shorty intake?

Re: Freshly rebuilt Moby 50V idle issue

Jim Swain Jr /

I have some stock shorty intakes and some shims. I have a malossi shorty intake with a 15/15 sha on it too that’s non running and in rough shape but the carb and intake is pretty much brand new.

I’ll figure out if I want to mount it on a shorty or on the long curvy.

Re: Freshly rebuilt Moby 50V idle issue

If carb doesn't work. Double check that your crankseals are in correctly. Spring facing out or away from the crank.

Or u may have already but something to think about

Re: Freshly rebuilt Moby 50V idle issue

Jim Swain Jr /

Yeah that was done correctly. Made sure of all that 100%

Re: Freshly rebuilt Moby 50V idle issue

Jim Swain Jr /

Dellorto 14/12 mounted onto a mallosi shorty intake we have great idle.

Take it down the road and immediately starts to bog down and die.

Flooding I’m guessing. Too rich. Stock 57 jet. Should I try without some of the mesh screens or down size my jet?

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