Hey guys, I just installed a cam and set of heads on a 350. When I try to start it, fuel spits up through the carb when the motor tries to hit. any advice?
You don’t say what year your camaro is. Some older GM 350s had different firing orders. The cam lobes for those cylinders were also reversed. Make sure your firing order and camshaft match.Even if your distributor cap is numbered wrong you can still use it,just place the wires in the right order. Of course there could be lots of other reason for backfiring- bad ignition, bad timing, low fuel pressure, you could have installed a cam to radical to run in your engine or one that opened the valves so far they hit your pistons and your pistons may need valve reliefs to match your heads and cam.
does the engine try to “pop” thru the carb? sounds to me like the distributure is 180degrees off. it easy to do.
How wild is the cam?? Cams with “full-race” timing can make starting very difficult unless everything is perfect…The ignition timing being off 180 degrees is another likely suspect…
Sounds like it’s out of time.
The cam is very mild and not radical at all. The heads are 67 cc and has 4 relief dished pistons. I will re check the timing. I installed the dist with the cam and crank dots at the 12 o clock position, rotor pointing at one. I haven’t got it to run yet, the gas spitting up has me worried. Could I have the valves to tight?
intake valve adj could do this If they are still open on the compression stroke the wind will move back up through the carb.
It’s likely to be either; timing issue or float set too high or stuck.
You set the timing with #1 on the compression stroke TDC right?
Is it a gas stream shooting out or just atomized fuel being spit back out? A bad float setting can result in the same problem. Did you R&R the carb during the rebuild? If not, did it sit with gas in it for some time? Have you checked the float level?
I’m going along with TwinTurbo about the distributor being installed on the compression stroke, not a 180 out.
(On a side note TwinTurbo, I don’t know if you’ve ever seen that show that used to be on TV called American Hot Rod with Boyd Coddington. It just never ceased to amaze me that out of this entire shop full of car experts that when it came to getting an engine going they would always drop the distributor into an engine without verifying what cylinder was up, what stroke it was on, or anything else. They would then dink around for hours (and in one case days, followed by having to bring in an “expert”) wondering why the engine would not start.)
Top drawer engine builders take pride in the fact that when they turn the key, their engines start with no drama…It costs no more to do it right the first time…
It is not a stream coming out, it is more like a blast of air along with gas. I have backed the rockers off quiet a bit now, so I don’t think that is an issue. It has an elderbrock carb on it. How to check for a stuck float on them? Can the cam and crank be at 12 o clock and not on the compression stroke. Can they both be in this position on the non compresion stroke. Thanks
With cam mark at 12 o’clock number one will always be on the compression stroke. Number one exhaust stroke is cam mark at 6 o’clock and crank at 12 o’clock. Tell me your method for adjusting the valves and if the lifters are hydraulic or solid.
A stuck float will NOT cause fuel vapor to blow back up through the carb. Does it do this with the ignition disabled? If so, it’s not the ignition timing…
Try this, Remove the valve covers and turning the engine by hand, watch the rockers, in order, and when that cylinder is on the compression stroke, (no movement of either rocker) loosen the adjusting nuts until you feel a LITTLE rocker to valve clearance, like in a solid lifter engine. Repeat for ALL cylinders.
NOW crank it with the ignition disabled. Has it stopped back-pumping out the carb?? If so, connect the ignition and fire it up…NOW you can adjust the valves…
No it does not do it with the dist unplugged. I am checking the timing again, when it pushes my finger off of the cylinder, the rotor is at number one, but the balancer is showing about 16 degrees after. I am thinking that it is showing that because i am bumping the motor over with the key and it is going a little past the mark. I must have the distributor in a little wrong. I think, lol
Also, someone run this by me again, tdc is when i feel the most air coming out of the cyliner, then the rotor should be on 1, and the balancer on 0, is that correct?
You can rotate the distributor while cranking and try to find a sweet spot where it will fire up…Just leave the distributor clamp a little loose…Rotating the distributor in the direction the vacuum advance is pointing will advance the spark…
sounds like crossed plug wires.
I judge tdc by the timing mark being at 0 degrees and both valves on cylinder #1 being closed (you need the valve cover off to see this).
ok4450, those guys were hacks in a lot of ways! Most of those type of car and bike building shows leave you shaking your head in disbelief on a regular basis. I always wonder how the customer must feel watching the show about their car being built- assuming they know any better. I recall one OCC episode where they forgot the fuel tank bung and only noticed it when trying to install the shutoff after it was painted. Then they had to remove a large donut of pristine paint to weld it in. Nice touch up on a brand new, custom bike.
I asked about the way the gas was being ejected to determine if it was a backfire versus stuck float. A stream out the vent is a classic stuck float problem whereas a backfire is usually a belch of air and atomized fuel. It wasn’t clear to me from the original description.
Got it going, just a little timing problem. After the engine ran for about 25 minuites, i developed some blow by. Shut it off, let it cool down and started ti again, no blow by. Could this be a sign of a busted head gasket? Just does it when at about three thousand rpms and reving when hot.