Grande is running lean? Help

Alright. 1980 Vespa Grande, 30mph version, stock exhaust, carb and airbox.

Symptoms. Plug chops are showing that my ped is running lean. Hard to start...It will only start after it backfires! Once it backfires and it starts to idle, it will act like it is about to die, but then picks back up, and starts to idle fine. Once it warms up, it seems to run good. Of course, after the engine gets hot, (lean mix), it starts to bog. Also, it starts to die when I give it throttle, from a complete stop, but then takes off after i twist the throttle a little further. I checked for vacuum leaks, and haven't found one yet. I sprayed the carb, and decomp lever with starter fluid while it was running, and didn't find anything. I have cleaned the carb several times and checked the float to make sure that it isn't stuck. I am starting to think that I have a clogged exhaust, since it won't start until it backfires. But, would that make it run lean? I plan on getting a performance exhaust, 13mm carb and airbox soon, but until then, I won't this baby to run good! Any help would be freakin sweet! Thanks in advance!

Chris

The Bombardment Societ

Swarm and Destroy

Re: Grande is running lean? Help

How many miles on your Grande?

Is it stock, i.e. have you modified anything?

Re: Grande is running lean? Help

Chris

Take the top off the carb. Make sure the throttle slide is clean with no varnish and no burrs or rough spots on it. I take them off and polish them with "0000" steel wool. Also make sure the slide channels in the carb housing on either side are clean and clear of obstructions so the throttle slide can move up and down easily. Put a couple of drops of 30 weight oil on the slide before you put it back in.

While you have the carb top off, squirt some WD40 into the throttle cable and hold the cable end up so you can lubricate as much of the throttle cable as possible.

When you cleaned the carb, did you find and clean the "Idle Jet"? It is located in the aluminum carb housing in the opening that goes on the carb intake pipe. It is just under the vertical brass tube in the aluminum carb housing. You have to look into the engine side of the carb opening and tilt the top of the carb slightly away from you to see it. Squirt some WD40 on it and blow it out with compressed air. I use a tiny drill bit #74 to clear the gunk out, but I DO NOT drill it.

Does your carb intake pipe have the plastic cup shim. It may have come off with the carb, which is OK as long as you put it back. The bike won't run properly without this.

Also WD40 or grease the throttle slide on the handle bar. Twist the throttle and look under the throttle handle and you should see a little slide moving back and forth as you twist the throttle. Grease this or squirt some WD40 on it. Don't get WD40 under the rubber throttle grip. Also squirt some WD40 down the throttle cable from the top end. Don't take the cable out or you may have a tough time getting it back because of a frayed cable end.

Last thing is to start the bike and have it on the center stand. Use the adjusting screw on the cable just before it goes into the carb top to shorten your cable length a bit. It will make the engine run at a higher RPM so you may have to adjust it a little at a time cold and hot until you get it like you want.

Depress the choke lever on the carb. Twist the throttle, the choke lever should pop up freely.

Let me know if these things help.

Re: Grande is running lean? Help

You didn't say anything about whether you are using the choke or not... or does it get better or worse when you do use the choke ?

Thats the easiest way to test for leanness and richness... if flipping thr choke on makes it run better... then its too lean.

Re: Grande is running lean? Help

Chris

Thought of one more thing. Did you remove the float when you cleaned the carb. The float needle valve should be cleaned to make sure it has no varnish on it so it will slide up and down easily.

Also the fuel path from the banjo down through the carb housing should be cleaned of all varnish and gunk so you get a constant, even fuel flow. You should be able to hold the carb up to the light and see through the fuel path in the carb casing.

Also check the banjo pipe to make sure it is clean and free of obstructions. While you have the fuel line off, try the petcock in both Reserve and On position to verify you have good fuel flow from the petcock.

Re: Grande is running lean? Help

Fred,

It definately runs better with the choke on. And the chops are showing up lean too...It's lean man. Any ideas? What about the backfiring?

Re: Grande is running lean? Help

thanks Zippy! i will give those suggestion a shot, and i will let you know.

Re: Grande is running lean? Help

Ron Brown /

Chris,

Zippy asked if you had any mods. Do you? Is the airbox, filter, carb all stock? Are you sure you have a stock main jet? Have you checked for air leaks at the intake? Does your carb have a needle on the slide and if so, what notch is it in?

Ron

Re: Grande is running lean? Help

It is stock...I mentioned that in the original post at the top. I am going to do Zippy's check on the fuel line and petcock tonight. I ruled that out because my carb was flooding previously. There is no needle in the dellorto carb.

Re: Grande is running lean? Help

Ron Brown /

Chris,

Take out the main jet and look at it with a magnifier under a bright light to make sure it does not have any crud deposited in the hole.

Ron

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