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Fuel spray
Hi, I'm just getting to the point of tuning my car and hit , what I think, is a serious condition- read scary. I have fuel spraying out over the top of the stacks about 1/2 -1 inch. I'm thinking real fire hazard. I was hoping for some guidance to tell me to stop or "that's normal" in the beginning of tuning and ,maybe , what direction to go to remove the condition. I know I've read that a bit of fuel vapor can be seen over the tops when running but this is at idle.
Here's the set up and story- 48IDAs on a 306 with a Comp cam-112.0 separation/duration @.050 224-230. Stock compression and mechanical fuel pump -reg set to 3# pressure.Carbs are a basic Redline setup (em. tube f7,idle jet 70f10,main 135,air correct. 120. The engine starts and runs but I have been frightened to do too much more because of the fuel spray issue.What can I adjust to make it go away? Any help would be more than appreciated. Regards, Jon |
Jon,
The phenomenon you have mentioned, referred to as "reversion" or "standoff" should generally only happen at wide throttle openings and higher rpm. Your engine is certainly capable of being happy with Webers, and not as wild as some I've seen, including my cars. Have you synchronized the carbs correctly? Have you measured the manifold vacuum at idle? How much timing do run at idle? Have you used a wideband O2 sensor to measure your Air/fuel ratio? 70F10 seems a bit fat for a 306, how far out are your mixture screws at idle? |
Gary, I actually have done little. Probably most worried about this situation as being dangerous. I did set the timing at 10 degrees and played with the idle adjusting screws on the linkage. That seemed to reduce the problem somewhat-i.e. the spray wasn't quite so tall. It was actually about 2 inches on the rear left bank when I started. I read about the reveriion but that is when running. This is at idle as I said. This is new territory for me and I don't want to burn up the car so help is very welcome.Thanks Jon
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Jon,
You'll need to recurve your distributor 16-20 at idle, 32-36 at 3000 or so. For now just bump the timing up at idle to see, more timing increases idle speed which then allows you to close the throttle slightly. How rich is the idle out the exhaust? |
I think the mix is rich but because of the fuel smell from the carbs it's hard to tell. I am seeing some carbon deposits on the exhaust. Since some of this did lessen the situation with reduced idle what you suggest makes me feel better. I used an MSD dist and just installed what came in the box. Didn't worry about changing things. Just wanted to hear the engine fire and run. I think I'm idling at about 850 rpm now. Sorry, I'd like to answer your other questions about sinking carbs,etc. but this excess fuel thing just locked me up.I'll try to get the idle down.Thanks,Jon
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What Idle air holder are you using?
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Rick, Idle jet holder is a 120 if that's what you ask. Jon
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You are putting too much fuel in on the idle circuit for the size engine. Try a 55 or 60 idle jet with a 100 holder, your standoff will disappear.
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Rick, I'll take your recommendation and get the parts. This change wouldn't cause any fuel starving on acceleration would it? Regards, Jon
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It will run on idle system to about 2700-2800 RPM. Leaning out idle system should get rid of fuel standoff, lobe separation angle may have something to do with it but I'm betting jetting Change will help a lot.
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Rick, I looked at what I got as spare parts and I have the idle jet you suggest BUT the idle jet holder , from a parts blowup, appears to just one holder #77903.120. Can you elaborate on the 100 size you suggested... and maybe where I can find it? I looked at Pierce,Redline,Weber Direct .... and they have nothing . Regards, Jon
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Jon,
Here's a listing in Australia: Products | Hardiman I'd buy a set of 50 idle jets, a set of100 holders and a number drill set (61-80) or preferably a metric set (.3 - 1.5) and drill you own combo. When you find the right size from experiment, you can then buy the "right" jets. And another link that maybe of interest to you: JayCee enterprises - Â Â Â Â Â Webers by JayCee |
Gary, Can't believe you guys in Australia are the only ones to have this part. I need to call some one rather than just looking at their web site. Thanks for the sku number. That will give me someplace to start. I do have drill sets ( just number not metric) and thought about drilling that third hole on the emul tube but I need to find some clear instruction for that. As I said to start in this post I'm just learning- excited and frightened to death at the same moment. Thanks again, Regards, Jon
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Jon,
Do you mean drill the third progression hole? |
Gary, Yes, that hole. Sorry if I use the wrong term. Just learning about all these pieces that need to play well together. I did speak with someone at Pierce Manifolds and ,of course, they supplied me the 100 holders. It also just dawned what you meant by your comment on getting a bunch of jets and a drill set. Maybe I'm just getting old and slow on the uptake- drilling my own sizes..Regards, Jon
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The last 3 digits of the part number denote the size IE:xxxx.120 or xxxx.100
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Any progress Jon?
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Got the smaller idle jets and plan to fit them today.Pierce didn't have any on hand but drilled out some at the same price. It's pouring rain here (NC,USA) and the car is still a go cart stage. With the way the fuel was spraying I have not wanted to start it inside my garage so I've got to wait for clearing before a start. I'll report back, Thanks, Jon
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Gary, I installed the smaller jets and holders. It appears to work. Started with a 65 and then reduced that to a 55. I still get a bit of a spurt from one of the stacks but ,overall it looks good. I'm assuming that the one carb still throwing fuel is just some different setting that I can correct. I now feel safer to move on to balancing the carbs without the fuel spray in my face. Regards, Jon
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