I have a vaporizer carburetor on my '27 Touring which was running great. The other day I was out and about and slowed down to make a turn; when I throttled back up it started missing and backfiring. If I run it slow it seems OK but as soon as I increase the throttle and timing (as shown in the book) it starts missing and backfiring. Any ideas?
Low on gas?
Dennis, if you are running gas with ethanol, drain your carb and sediment bowl and see if that helps. I run e10 all the time but once and a while have to do a drain down. KGB
Check the sediment bowl & screen for "sediment" blocking flow. Almost said "crap". LOL
Thanks for the quick replies.
The fuel tank was full. I did drain the bowl and check the screen before asking for help. It seems to be getting plenty of fuel.
Just sat from working on a vaporizer carb. There was a hole the size of a quarter in the little thin heating plate. It had air passages plugged with rusty crap. It is running real sweet right now. Good luck to you!
How is the air flow? Is the butterfly valve spring weak?
Sounds like the plate. Even a pin hole can cause trouble. Take it off and hold it up to the Sun. A hole will show up immediately.
That's about what mine did once. I found a crack in the plate. It opened up and got worse when hot. The vaporizer had been great for 10 years. I ended up using a Stromberg until I figured out what was happening. New plate and no leaks = happy T.
Thanks again for all the suggestions. As soon as I get some time I will try the ideas mentioned.
I finally got a chance to look at the '27 Touring with the vaporizer carb. This is what I found:
1) No hole or crack in the plate.
2) Butterfly valve seems to function Ok.
3) No plugged passages
4) Found oil on the plate and in the intake.
Could this be a broken piston ring?
Bad Head gasket?
Dennis, You said when you increase the throttle and timing the miss happens. Did you look at the wires to the timer ....do they all have clearance when the timer is rotated?
Yes, I checked the wires to make sure they didn't touch anything when I increased the throttle.
I guess I'll pull the head when I get time.
Before you do that you ought to check the inside of the timer. If that is OK, look at the spark plugs. Then do a compression test.
I finally got a chance to look at the problem in detail. I did a compression test as Royce suggested and found little to no compression in #1 cylinder. Pulled the head late Sunday and found a broken vale spring pin on the intake valve of #4 cylinder. Cleaned up all the carbon from the pistons and head and I am getting ready to put everything back together but before I do is there anything else I should look for. Everything else looks good. I should mention that this car had a valve job (new valves,springs,retainers,and pins about 3 months ago). My concern now is did I get a group of bad pins or was just one weak and snapped.
I don't think some of the pins are as good as others, I use cheap drill bits and make my own. By cheap I mean ones I find at flea markets and such. KGB
I have not found a problem with the vap systems yet, thought there was one a time or two but was always a fuel or wire problem. Have two cars that have run several years and national tours with vap's.
You said "little to no compression on #1 cylinder" but you found the broken pin on #4 intake valve. You need to find out why #1 had no compression before you put it back together. That is unless you mis-typed the cylinder with no compression.
Ifn you have one bad pin, you should check the others to make sure that they're OK and not ready to fail. There was a bad batch of (soft) pins a few years ago. I make my own out of drill rod.