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Old 12-05-2009, 08:53 PM
wolf_walker's Avatar
Zen And The Art Of Diesel
 
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Location: Oklahoma City
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Question Solex revisited, 1500rpm miss

I finally got my VW up and moving and was able to spend some time on the original 4A1 for the 280 this weekend. It was warped as usual, I ended up plaining by hand and checking with a feeler gauge and straightedge, and eventually it's not leaking externally or in the primarys. I set the float level
with the hip roof float at +2mm per the book when using the later pressure regulating dealy at the carb inlet. Mucked with the choke till it starts, mucked with the idle mix screws for fastest hot idle, set idle to 900rpm ish with the main screw. Set accel pump pre-load at 1mm. Set the idle assist diaphram clearance to 1mm from the linkage arm and it's hose-off speed to 1400 or so.
Set fast idle hot to 2400rpm.

So it idles, in and out of gear. It start. It don't leak. After a bog I can likely fix WOT works well enough. Trouble is, and has been more often than not, a miss or rough spot at 1500rpm. To induce this, one slooowly opens the throttle from idle in P and as it comes to about 1500rpm, it starts to bog and miss. I don't think it's an accel pump issue because I verified it works visually and rapping the throttle quickly the engine responds normally. Also during this rpm specific bog you can back off and on the throttle and it will pull through it, or just move the accel linkage further and it will clean up. It seems to be JUST right around that rpm. In motion, the rpm and such is a little different I think with load on it, but it's still there, ends up being from around 50mpg on up to 65 or so where it clears up, mostly.

Does this thing transition from idle circuit to low speed at this RPM? I'd have thought it would be lower. Only other thing I can think to try is try and lock it in at the missfiring rpm and adjust the idle mix screws there maybe, see if that helps. Ran out of time tonight. I dont' think it's an ignition issue as it's that one specific rpm like that. Dwell was where it should be last time I checked not long ago, points clean, new plugs, wires good. I think I have the timing set static to 0BTDC, the ignition retard is dissabled since the control mechinism wents nuts awhile ago and was clicking retard on and off on cold start and generally making life miserable.

I'd really like this thing to work just on principle, and so I could put some attention and money toward other parts of the car(if nobody buys it). Webbers are too costly, I'm not in love with the idea of trying to make a Quadrajet work on a small motor like this, and a cheap 2 barrel seems a less than ideal solution as well. I'm still leaning toward TBI of some sort, but that's going to be a project to say the least.

Thoughts?

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Old 12-06-2009, 03:17 AM
4x4_Welder's Avatar
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Sounds more like an ignition problem. The idle-main transition is based on throttle position, not RPM. Being at a specific rpm, I'd be inclined to think it's the mechanical advance sticking.
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Old 12-06-2009, 01:37 PM
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Zen And The Art Of Diesel
 
Join Date: Dec 2003
Location: Oklahoma City
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Quote:
Originally Posted by 4x4_Welder View Post
Sounds more like an ignition problem. The idle-main transition is based on throttle position, not RPM. Being at a specific rpm, I'd be inclined to think it's the mechanical advance sticking.
I'll check it, was clean and free last time I looked but you never know.

Only other thing I can think is maybe I should let the carb body soak in a gallon
of that cleaner since it's so hard to actually get to the transition passages.
Or, the idle mix screws need to be set other than to highest idle/vacuum like most carbs maybe?
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Old 12-10-2009, 01:25 AM
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Zen And The Art Of Diesel
 
Join Date: Dec 2003
Location: Oklahoma City
Posts: 2,050
I finally found that miss. The primary's don't start metering fuel till 1500rpm, right where that miss starts, and when they do meter they aren't misting fuel, possibly because of what passes for a venturi in this POS carburetor can't work at the level of airflow, the fuel just dribbles and blobs out. This is why it's always cleared up when I went into the secondary's, even just a hair.

I give up, I'm done, no more with these carbs. It is a bad, bad design.

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