'71 250 Backfiring through the Carbs - Benzworld.org

MB250 · 07-20-2005, 04:22 PM

Well, I just got my 1971 250 back from the mechanic and was taking all the trim off getting it ready to be painted and now it's developed a new problem. It seems that when I am on a hill and the car is in a forward gear she backfires through the carb and then dies. I can put her in park and start her back up again and she idles fine but once put in gear again the same thing happens again, she backfires through the carbs and dies. I just had the whole ignition system gone through new plugs, wires, distributor cap, and rotor. Any thoughts would be appreciated.
Thanks

ggenovez · 07-20-2005, 06:03 PM

Check your timing and you may be running too rich. check the colour of the plugs. Hope that helps.

MB250 · 07-23-2005, 09:21 AM

I checked the timing and it seems to be good ( thanks to help from ggenovez) when I took out the spark plugs which are brand new, they were covered in carbon deposits! Which indicate a rich mixture and can cause hesitation, misfiring, and hard starting which are all symptoms my car has. So I guess I am going to go try and fix my carbs which is the most likely thing that is causing the backfiring.

MB250 · 07-23-2005, 09:29 AM

This is most likely the problem
http://jaimekop.com/CarbManual/Page08-09/index.html

ggenovez · 07-24-2005, 06:07 AM

Rich mixture is usaly adjusted from the fuel mixture screw http://jaimekop.com/CarbManual/Page14-15/index.html

If you are going to adjust the float make sure you have a minor carburator rebuild kit in hand in case it starts to leak. Last thing you want if fuel running on your exhaust pipes.

MB250 · 07-24-2005, 01:33 PM

Thanks I'll check it out, good point about the rebuild kit, not a bad idea to always have one of those handy.

pm220b · 07-24-2005, 05:26 PM

Hi MB250, Check out my new post titled more adjusting solex & timing. I had a very similar problem and ended up screwing the mixture screws almost all the way in and advancing my timing considerably and it runs much better and has good power on hills but I'm still looking for answers on why it is this way. I'm sure it isn't right but it runs pretty good. I suspect my mixture screws are bad. If you have found the answer and yours is straightened out I would love to hear how you did it. Pat in NH

doc_rage · 07-25-2005, 06:31 AM

Does that have a points ignition system? If so, check the dwell on it as well.

I was having problems with backfiring through the carb as well when I would get on it and after adjusting the dwell, it cleared it up.

MB250 · 07-25-2005, 04:13 PM

I still haven't fixed it, I think i have figured out that it is not the carbs though because I rebuilt both of them and it still runs the same, I checked the timing and that was correct. Now the dwell, I have no idea what or how to play with that but I suspect it to be the root of my problem because it has done this in the past and looking through old receipts from the dealer the thing they did to fix it everytime was to set the dwell and adjust the timing. If anybody could tell me what dwell is and how to set it or advance it I would surely apprectiate it. By the way the ignition system is points.
Thanks

MB250 · 07-25-2005, 04:14 PM

By the way Pm220b it sounds like our cars have the same problem, because this is a re-occuring problem for my car.