Smallframe 19 Carb Trouble

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toigo
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Smallframe 19 Carb Trouble

Postby toigo » Mon Mar 24, 2014 6:52 pm

So the smallframe is running, but I'm pretty sure it's running too rich. Here's what's going on.

  • It only runs decent at more than 3k rpm and even then it's not nearly as powerful as it should be.
  • It's miserable to start and the only way I can get it started is with a lot of kicking with the throttle wide open and the gas off because it seems to be flooded.
  • It runs even worse with the choke pulled when it is running.
  • It runs better with the air filter completely off. I can see it kicking out some gas with the filter off too.
  • I've played around with the timing and it doesn't seem to make too much of a difference. I haven't been able to get the bike running well enough to even get it dialed in.
  • Idle adjustment mix screw doesn't make any difference.
  • Spark plug is also wet.
  • I've been on a bike that's been jetted too rich (after another rebuild) and the poor performance feels similar.

It's the same carb described here: http://website.lineone.net/~smallframes/carb.htm

So my guess is that something is screwed up with the carb and it's dumping too much gas into the intake manifold. This is a 19/19 carb which I don't think was stock on a 66 Blue Badge, but is pretty common. The same setup was working pretty well before I converted the bike to 12v ignition and rebuilt the engine. I also dipped and completely cleaned the carb. The same jets are in it that were previously working fine.

Main = 74 (top of the bowl center)
Idle Jet = 42 (screws into the side of the carb)
Starter Jet = 60 (top of the bowl off to the side)

My guess would be that the needle or float were screwed but they both look fine and the float can go high enough to push the needle to close out the hole to stop the gas from coming into the bowl. Also tested that pushing the needle up shuts off the gas flow properly. I'm pretty stumped if anyone's got any ideas. Everything I can see tells me that the float or needle isn't working properly, but everything looks fine.

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Zeets
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Re: Smallframe 19 Carb Trouble

Postby Zeets » Tue Mar 25, 2014 8:48 am

Float sounds like you're on the right path. Its not uncommon to have dirt or something in the fuel system obstruct the needle and cause it to leak. Also, the float itself can have tiny pinholes in it that will allow it to sink and keep fuel flowing. Also, float adjustment can be an issue... it the float requires too much travel to close the needle it can seem like a stuck float or heavy float. Usually you hold the carb upside down and make sure the float looks level to the carb, but I don't know the vespa specific float adjustment. If its the original needle, it can wear into the hole, and require too much pressure pressure to properly seal, it'll usually have a groove worn into it radially. Also, if its the original needle, the rubber tip may not be compatible with this E10 the farmers have forced into our gas tank and it can swell or disintegrate.
Zayretow

70' Vespa Sprint (2009 LML power)
74' Yamaha RD350 (pinger)
2008 Suzuki DRZ-400SM (thumper)

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imjuanpablo
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Re: Smallframe 19 Carb Trouble

Postby imjuanpablo » Tue Mar 25, 2014 12:41 pm

Do you have the felt ring on intake manifold? intake manifold proper otherwise?

Forget the proper jetting.......last oen I worked on was the ECC raffle bike, and it was kitted with a expansion pipe......


here is a pic, it's #56

P.S. I hate working on smallframes.

Image
John F.

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toigo
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Re: Smallframe 19 Carb Trouble

Postby toigo » Tue Mar 25, 2014 1:48 pm

Yup, small white felt washer snug where it should be and I oiled it to help it seal better. I can maybe get that manifold off with the engine in there, but it should be good. If something there wasn't sealing proper I'd be running lean though right?

Thanks for the diagram, I'd been looking for one and couldn't find it.

Yup... smallframes.... never again. This one was too good of a deal to pass up, but it has been a pain in the ass. Praying that I won't have to take the engine back out of it and the ultra low location of the gearbox isn't fun either if you don't have a lift.

I'm going to mount the carb on my work bench with a full fuel line to it and see if it keeps sucking gas down or shuts off properly. Hopefully I can see if fuel is being forced up through the main jet into the venturi even without any air rushing through it cause my suspicion is that this thing is just constantly leaking gas into the manifold with or without any pressure pulling on the engine side of the carb.

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Mikeh
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Re: Smallframe 19 Carb Trouble

Postby Mikeh » Tue Mar 25, 2014 4:33 pm

You may also want to check your points gap and the sparkplug.

My allstate was having some tough starting but now it starts on the first kick.. even when the motor is cold.



I too was stumped I started with rebuilding the carb again and even trying another carb.. and it didn't make a difference. The motor barely started. I then pulled the motor back out of the frame and checked it all out in more detail. I was very close to splitting the cases to check the seals. But I did an oil leakage test and it passed.. so I was still stumped.

I then checked the points gap and it was a tad wide. Be aware that you need to use the METRIC settings on the points gap.. not the inches.. for some reason the inches values don't line up with the metric values from the manuals and you end up with a gap that is way too wide to give a good spark. It will spark.. but it won't be super strong like it needs to be. Make the gap just under the minimal gap that is specified in the manual and you will have VERY strong spark.

I did this and then the motor was able to be started much easier. (I also used an electric drill with a socket mounted to it to turn the motor rather than kickstarting it.. this saved my leg).

Then once I got it pretty good then I started checking plugs out.. I went to the advance auto parts place and they let me walk back to the wall of spark plugs and I picked out a few to try. I got an NGK B5, B6, and B7. The B5 seemed to work best.. it's a tad of a hot plug for the scoot.. but I am not racing it so I am not worried about melting the motor - and it starts super easy with it.

Good luck with it.

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toigo
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Re: Smallframe 19 Carb Trouble

Postby toigo » Tue Mar 25, 2014 4:52 pm

Thanks Mike. The bike is converted to use the P200 style flywheel and CDI and the spark looks pretty solid. I also swapped a known good CDI on it and it still have the same issue.

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Mikeh
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Re: Smallframe 19 Carb Trouble

Postby Mikeh » Tue Mar 25, 2014 5:15 pm

Got it. That's good.
But don't overlook the plug though.. at least try that out.

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12CI
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Re: Smallframe 19 Carb Trouble

Postby 12CI » Tue Mar 25, 2014 7:45 pm

according to this site, the jets you have sound about right; maybe one or two sizes big, but not grossly excessive.

random thoughts:

since it ran OK with these same jets before you cleaned the card, then possibly a jet was damaged whilst cleaning (bore enlarged)

maybe prior to your rebuild, there was some problem (excess air from somewhere, or maybe some crud in the carby or something) that a previous owner accommodated by installing an oversized jet. now that you have it back to spec, the oversize jet is hurting you.


remember that too rich could be too much fuel, or not enough air.
did you do anything to change the airflow? new filter materiel?
if it were a largeframe, i'd suggest you clean the mouse nest out of the bellows...
as shameless as I am tactless and guileless

dirtyhandslopez
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Re: Smallframe 19 Carb Trouble

Postby dirtyhandslopez » Sun Mar 30, 2014 5:40 pm

Looking at what you did before the motor started acting up, perhaps the timing is off, kinda the same thing Mike is talking about.

Also,if memory serves , isn't the ignitor section(where the magnet fingers are overlapping) in a different spot, in relation to the flywheel woodruff key slot,for P's and
smallframes?

You may be lining up your timing marks for P timing instead of SF timing....
That's not going anywhere

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toigo
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Re: Smallframe 19 Carb Trouble

Postby toigo » Sun Mar 30, 2014 6:18 pm

Thanks for the help everyone. I've got new main jets on the way and want to try that before I get into playing with the timing too much. I also confirmed that the float/needle is working properly. With the carb off the bike and the fuel line attached. I can shake the carb and once the float bowl is full no more fuel is getting drawn into the carb so it would seem that the needle seals off just fine when it should. I've got a clear fuel line on there so I can see for sure as well. Also didn't see any excess fuel getting pushed into the carb barrel the way I expected too if the float or needle was bad.

The kit I've got is the ScootRS one here which is of questionable quality as well. I swapped my known good CDI into the mix though just to take that out of the equation too. I have the case and flywheel marked out for 21 degrees before center which I think should be about right, but I haven't even been able to get the bike running well enough to check how close it is. I think stock, the bike is 24 degrees (125 cc smallframe), but I had read that when switching to a CDI from points it happens a little faster so you actually want to retard the timing about 3 degrees to keep everything where it should be.

http://scootrs.com/moreinfo.cfm?Product_ID=2132

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toigo
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Re: Smallframe 19 Carb Trouble

Postby toigo » Sat Apr 05, 2014 5:21 pm

So I put a brand new 74 main jet in the carb and still had the same behavior. I think I've got if figured out though. I pulled the flywheel off and looked at where everything was (the pickup on the stator and where I think the polarity on the flywheel changes) and from what I could see it look like the spark would be firing very close to top dead center rather than the proper amount before it.

I had previously moved the stator all the way advanced that it would allow with the slot it had in it. I cut off a piece of the stator which let me rotate it about 10 degrees earlier and the performance of the bike felt just like it should for the most part. It's still not right where it should be and wants to die under about 2k RPM, but the performance for anything above there feels like it should. I'm going to try to figure out around what the timing is currently before I start cutting more of the stator off though just incase changing the timing is compensating for something else being screwed up in the bike.

So next question. Timing lights. I've got one of these:

http://www.amazon.com/INNOVA-3551-Inductive-Timing-Light/dp/B000EVYH72/ref=sr_1_1?ie=UTF8&qid=1396732538&sr=8-1&keywords=timing+light

and can't get it working. I'm trying to get it to work on a reliable bike (my P200) first. I've got the red and black aligator clips attached to the battery and the inductive clip attached to the HT lead running to the spark plug. There's an on/off button, but I never see the strobe flash. It makes a slight buzzing sound when the power from the battery is running to it. Am I missing something? I'm probably going to pickup another one to see if this one is just a dud.

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toigo
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Re: Smallframe 19 Carb Trouble

Postby toigo » Sun Apr 06, 2014 9:57 am

Confirmed that my timing light was shit. Borrowed a friend's and it worked just fine.

dirtyhandslopez
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Re: Smallframe 19 Carb Trouble

Postby dirtyhandslopez » Wed Apr 09, 2014 8:56 am

Why are you worried about what the timing is now? It's not running correcly....
Timing right at 20-21*btdc will probably be where it'll end up running best if it is not a tuned motor. If it is tuned, you may want to run at 18-19*btdc possibly even 16* if it is highly tuned.
That's not going anywhere

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toigo
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Re: Smallframe 19 Carb Trouble

Postby toigo » Fri Apr 18, 2014 8:57 pm

So the timing is where it should be and I'm pretty sure I'm that I'm dealing with an air leak now. The bike makes plenty of power, but runs hot and the idle shoots up occasionally if you're in neutral and will go back down once you put it in gear. Still miserable to start as well since I think it's drawing through where the air leak is and not pulling enough gas from the carb.

If I spray carb cleaner where the intake manifold meets the engine there's no affect. If I spray carb cleaner where the carb mounts onto the intake manifold the engine immediately dies. So something is not sealed correctly there. I've got the greased up felt washer in the sleeve and have even sealed the slits on the carb with gasket maker. Also tried wrapping the end of the carb in pipe thread tape as well, but still the same issue no matter how hard I torque down the ring around the sleeve.

Pretty much running out of ideas at this point. The fit between the manifold, carb, and sleeve seems nice and snug. From reading up on this it seems to be a definite problem spot on smallframes. Anyone got any other suggestions on how to seal this properly? The only other thing I can think of is one of the pieces involved is warped or cracked potentially or there's something wrong on the carb itself.


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