OP
@whereshaldo avatar
UTC

Hooked
Stella 2T 150, Honda C70
Joined: UTC
Posts: 422
Location: Seattle
 
Hooked
@whereshaldo avatar
Stella 2T 150, Honda C70
Joined: UTC
Posts: 422
Location: Seattle
UTC quote
I'm cruising along this morning to work in 4th at somewhere around 18th - 1/4 throttle and look down and see my temp has spiked from 225 or so up to 356 in a matter of about 10 seconds. I pull the clutch and watch the temp drop a bit and then drop it into 3rd bringing up the revs and the temp immediately settles back down to the mid 200s.

I think this indicates that I still may be too lean on my idle jet. I recently switched from a 55/160 to a 48/140 and I think the lesser volume is making me too lean. The AF ration of a 48/140 is 2.92 vs 2/91 for the 55/160 which isn't that different but it also is flowing less fuel overall, correct?

I really need to get the 50/140 and 52/140 on order.

H
@chandlerman avatar
UTC

Lucky
76 Sprint V, 63 GL, 62 VBB, 05 Stella, 66 Smallstate, 79 P200E, 66 Lammy S3
Joined: UTC
Posts: 9979
Location: Nashville

78 Days Since Last Explosion
 
Lucky
@chandlerman avatar
76 Sprint V, 63 GL, 62 VBB, 05 Stella, 66 Smallstate, 79 P200E, 66 Lammy S3
Joined: UTC
Posts: 9979
Location: Nashville

78 Days Since Last Explosion
UTC quote
You sure you haven't sprung an air leak?

Alternate cause would be that you're getting fuel starved and leaning out as the float bowl or float bowl passage can't keep up with flow.

Neither one is good, obviously.
OP
@whereshaldo avatar
UTC

Hooked
Stella 2T 150, Honda C70
Joined: UTC
Posts: 422
Location: Seattle
 
Hooked
@whereshaldo avatar
Stella 2T 150, Honda C70
Joined: UTC
Posts: 422
Location: Seattle
UTC quote
I think what is happening is that I'm rolling along at 40 mph or so but the throttle is closed enough that i'm just rolling along with some engine load but absolutely no fuel beyond the idle circuit. I'll do another experiment tonight and see if i can replicate it or if I accellerate through it if the temp comes down.

The issue is happening very early in the opening of the throttle. I can run WOT and it will get warm but it doesn't spike like it was doing this morning.

I would be really surprised if it was an air leak. I have no other symptoms indicative of an air leak. It idles low and steady, accelerates well, returns to idle quickly.

H
@ginch avatar
UTC

Veni, Vidi, Posti
74 Super, 75 Super, PX project, LML off-roader and '66 Blue Badge Smallframe
Joined: UTC
Posts: 8697
Location: Victoria, Australia
 
Veni, Vidi, Posti
@ginch avatar
74 Super, 75 Super, PX project, LML off-roader and '66 Blue Badge Smallframe
Joined: UTC
Posts: 8697
Location: Victoria, Australia
UTC quote
Happened to me some time back. What I eventually worked out was that the timing (stock stator) was rock steady up until maybe 4000rpm. Then it went crazy with the timing light showing it plus or minus 15 degrees on the 18 I had it at.
Fortunately it was only a Polini 210 that was bound to implode at some point anyway.

Might be worth checking, however far-fetched it seems.
@charlieman22 avatar
UTC

Nedminder
62 VBB1T Round Tail W/ leaner sidecar
Joined: UTC
Posts: 4110
Location: california
 
Nedminder
@charlieman22 avatar
62 VBB1T Round Tail W/ leaner sidecar
Joined: UTC
Posts: 4110
Location: california
UTC quote
Haldo - couple questions/ comments.
- I'm always surprised how much more open the throttle is than I perceive. How fast were you puttering along when you saw the spike?
- can your remind: is your carb drilled?
- have you pulled your spears plug to see what it looks like?

Here is a pic of mine.
It is crusty with many layers at this point - all of them nice and chocolate like in color. This is as lean as you would want to be.

Good to do this in daylight to give a sense of how your set up is running.
I'm suspicious more of your main jet than your idle - but I'm guessing.
Forum member supplied image with no explanatory text
@charlieman22 avatar
UTC

Nedminder
62 VBB1T Round Tail W/ leaner sidecar
Joined: UTC
Posts: 4110
Location: california
 
Nedminder
@charlieman22 avatar
62 VBB1T Round Tail W/ leaner sidecar
Joined: UTC
Posts: 4110
Location: california
UTC quote
* also - remind: is this a BGM with a temp guava in the head rather then under the plug?
OP
@whereshaldo avatar
UTC

Hooked
Stella 2T 150, Honda C70
Joined: UTC
Posts: 422
Location: Seattle
 
Hooked
@whereshaldo avatar
Stella 2T 150, Honda C70
Joined: UTC
Posts: 422
Location: Seattle
UTC quote
I do think my MJ is lean still. I'm running a 125 and its too lean, 128 is too rich. I have 126 and 127 showing up today. Its certainly possible that the throttle was open more than i thought and if I'm coasting under engine compression it could be building enough vacuum to transition fully over to the MJ but not enough fuel to fully lubricate things.

I'm running a temp gauge under the spark plug, compression ring removed from the plug.

I have not been able to replicate this behavior, so who knows!

H
@charlieman22 avatar
UTC

Nedminder
62 VBB1T Round Tail W/ leaner sidecar
Joined: UTC
Posts: 4110
Location: california
 
Nedminder
@charlieman22 avatar
62 VBB1T Round Tail W/ leaner sidecar
Joined: UTC
Posts: 4110
Location: california
UTC quote
Perhaps shoot a pic of the spark plug in daylight as I've shown.
Will help us get a read on things.

Is carb float bowl drilled?
What cylinder?
OP
@whereshaldo avatar
UTC

Hooked
Stella 2T 150, Honda C70
Joined: UTC
Posts: 422
Location: Seattle
 
Hooked
@whereshaldo avatar
Stella 2T 150, Honda C70
Joined: UTC
Posts: 422
Location: Seattle
UTC quote
20/20 Carb is drilled to 2mm. BGM177, SR Race Exhaust, P200 drilled air filter.

A 24/24 is like $50 on ebay and I'm tempted to just bite the bullet. Way cheaper than a new jug. I realize I'm then starting over on jetting but I feel like I'm fighting overall mixture volume in a way that I am struggling to overcome with the 20/20.

H
Forum member supplied image with no explanatory text
@charlieman22 avatar
UTC

Nedminder
62 VBB1T Round Tail W/ leaner sidecar
Joined: UTC
Posts: 4110
Location: california
 
Nedminder
@charlieman22 avatar
62 VBB1T Round Tail W/ leaner sidecar
Joined: UTC
Posts: 4110
Location: california
UTC quote
Ok. That's helpful.
A side shot of the plug would also be good (sorry!)

Your plug looks new - so it takes some time to color up.
That said, you don't look wildly lean.

Going up in main jet can not hurt you.
Ideally- you start with a main that's big enough so it just won't rev out (shaves at least 1000 rpm off your max).
Then walk down to an optimal jet size.

The ring around your plug (see my example below) should go to a charcoal.
This is mostly swayed by your idle jet.
Yours is wet, but not fully colored yet.

One trick I like to use is to utilize a colored (used) plug.
You can take a before pic for your own record, then ride it before pulling and looking again.

This is a general rather than super specific test.
If you want to improve that, too specific, you run it at a certain throttle position, say wide open, for example, in third, for a good five second count, and then you immediately shut off the motor without letting it idle, coast to a stop, pull the plug, and shoot a picture. This will give you a very specific reading of your main jet.

How many miles do you have on the motor?
Forum member supplied image with no explanatory text
OP
@whereshaldo avatar
UTC

Hooked
Stella 2T 150, Honda C70
Joined: UTC
Posts: 422
Location: Seattle
 
Hooked
@whereshaldo avatar
Stella 2T 150, Honda C70
Joined: UTC
Posts: 422
Location: Seattle
UTC quote
I just rolled past 7300 but I've got about 1000 miles since i replaced the rings and fixed all my air leaks.

Jets arrive tomorrow and the plan is to move up to the 127 and see if it will rev out or if I get spluttery. If spluttery then down to the 126.

Plan is also to get some new plug and do some chops at some point.

I'll keep fiddling.

H
@charlieman22 avatar
UTC

Nedminder
62 VBB1T Round Tail W/ leaner sidecar
Joined: UTC
Posts: 4110
Location: california
 
Nedminder
@charlieman22 avatar
62 VBB1T Round Tail W/ leaner sidecar
Joined: UTC
Posts: 4110
Location: california
UTC quote
Sounds good.
For what its worth - I find I can do "plug chops" without chopping any plugs - using the method I noted above.

I like to find a slightly uphill area - creates more load on the motor.
Run it and kill it to coast down.
Pull plug.

Used plugs color up much quicker than new - and you will be surprised how quickly you can get color CHANGE on a used plug - vs NEW color on a new plug.

My $.02 to add to your existing arsenal.
@ray8 avatar
UTC

Molto Verboso
Joined: UTC
Posts: 1893
Location: Los Angeles
 
Molto Verboso
@ray8 avatar
Joined: UTC
Posts: 1893
Location: Los Angeles
UTC quote
whereshaldo wrote:
20/20 Carb is drilled to 2mm. BGM177, SR Race Exhaust, P200 drilled air filter.

A 24/24 is like $50 on ebay and I'm tempted to just bite the bullet. Way cheaper than a new jug. I realize I'm then starting over on jetting but I feel like I'm fighting overall mixture volume in a way that I am struggling to overcome with the 20/20.

H
I thought you had a 24/24

That $50 ebay carb will be shit.

The BGM faster-flow (reworked Spaco) is $$ but it will save you much frustration, time and disappointment.
Aside from the the carb bowl channel to the mj, there's another restriction in the float assembly on a stock carb that is dealt with as well.
It will run cooler/use more fuel, fwiw.
"Should" be PNP with the jets it's shipped with and the mj's you probably already have

I've never had a CHT spike like that, though, except with an uphill 100F 0-oil "event" (gasket-blocked autolube channel Facepalm emoticon ). An air leak will climb and never settle, not suddenly spike like that.
Had to be an "event" spike vs your current jetting, like (wild guessing) you entrained a big-ass bubble into the oil tube when you worked on the carb.

As far as 1/4 throttle, no main circuit fuel:
The main circuit is vacuum triggered. At 40mph 20/20 carb 1/4 throttle it's online.

Original Dellorto on the left.
Original Dellorto on the left.
OP
@whereshaldo avatar
UTC

Hooked
Stella 2T 150, Honda C70
Joined: UTC
Posts: 422
Location: Seattle
 
Hooked
@whereshaldo avatar
Stella 2T 150, Honda C70
Joined: UTC
Posts: 422
Location: Seattle
UTC quote
I am actually somewhat suspicious about the oil. After I had the soft seize I noticed a huge bubble in the oil line. I've been pulling the cover and checking daily and no more bubbles in sight but that doesn't mean I'm not missing seeing one. I am very cautious when assembling to make sure the holes in the gaskets for the oil passages are all clear and I rebuilt the oil pump on this last assembly. Everything seems functional but thats just the thing, its all workign great until it isnt.

Noted on the crappy 24/24. I think I'm super close, will wait and see what happens with these new jets I've ordered and then if I'm still struggling I'll get a proper carb from a reputable reseller.

H
OP
@whereshaldo avatar
UTC

Hooked
Stella 2T 150, Honda C70
Joined: UTC
Posts: 422
Location: Seattle
 
Hooked
@whereshaldo avatar
Stella 2T 150, Honda C70
Joined: UTC
Posts: 422
Location: Seattle
UTC quote
I spent half the day going though my carbeuretion and I think I have sorted out the temperature spike issues.

First off, I had used hondabond on the gaskets between the airbox and the reedblock and between the carb and the airbox. I don't think this is a good idea in hindsight. Even with the very spartan amount of sealant that I applied, it managed to goop into the oil passages when everthing got torqued together. I think some minor blockages of those oil passages were enough to cause some restriction in lubrication.

The reason I'd used the hondabond was in an attempt to limit the oil seepage into the airbox and eventually down the back of my engine. I dont' know if I fixed it -- time will tell -- but I rebuilt the entire oil pump just to make sure everthing was working properly and I polished the seat of the bypass valve. When I got everything back together I noticed that I was seeing some sticking in the oil pump cam (connects the throttle slide to the throttle cable and the oil pump lever arm). It would stick at mid pull. Starting the bike was exciting as it would immediately rev to 7k or 8k RPM. I pulled the pump apart again and found that the small bump on the inside of the pump housing was binding on the oil pump gear. I smoothed out the bump with a dremel and put everythign back together. I though that was the end of it but the throttle stuck open again scaring me and everyone within a 100 yard radius. In addition the slide rod pulled out of the hole in the pump cam.

So everythign came back out and in investigating I discovered that my throttle slide was bent or warped and was binding halfway through the pull. I luckily had a spare slide and so was able to put everything back together and its all running like a top. I now question whether the binding of the oil pump cam was really and issue. When the engine is running the pump gear is turning and this would mitigate the pump cam binding on the detent in the gear. I'm not sure how the slide got bent but its nice to finally find a couple smoking gun problems and resolve the issue.

H
@ray8 avatar
UTC

Molto Verboso
Joined: UTC
Posts: 1893
Location: Los Angeles
 
Molto Verboso
@ray8 avatar
Joined: UTC
Posts: 1893
Location: Los Angeles
UTC quote
It's a shame you didn't spring for the threaded sensor that sits mm from the center of the bowl I recommended on another thread of yours.
That alone makes the BGM superior the the VMC, along with a few other things.

Jetting via ride-feel and scary-accurate CHT.
Heat map of an air-cooled 2 stroke. I think this is an asphalt stamper.
Heat map of an air-cooled 2 stroke. I think this is an asphalt stamper.
DoubleGood Design banner

Modern Vespa is the premier site for modern Vespa and Piaggio scooters. Vespa GTS300, GTS250, GTV, GT200, LX150, LXS, ET4, ET2, MP3, Fuoco, Elettrica and more.

Buy Me A Coffee
 

Shop on Amazon with Modern Vespa

Modern Vespa is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to amazon.com


All Content Copyright 2005-2024 by Modern Vespa.
All Rights Reserved.


[ Time: 0.0167s ][ Queries: 4 (0.0060s) ][ live ][ 313 ][ ThingOne ]