By Zippy (Zippy) (152.163.213.81) on Monday, June 18, 2001 - 02:31 pm:

I'm going to put this in a few postings, my ISP kicked me off at the end of my novel, before I could post it, and I lost about half an hour of work.

Here's the story. At about 4000 rpm under load my engine starts misfiring horribly. If let way off the gas I can make it go a bit faster, but not much. Under no load I have taken it up to over 5000 rpm with no apparent problems.

By Zippy (Zippy) (152.163.213.81) on Monday, June 18, 2001 - 02:45 pm:

What am I running you ask? Ok '79, 1.2, 1.3 crank and rods, 1.2 pistons, EB3 ported and matched head, cut flywheel, balanced, 4-1 headers to 2" pipe, Edelbrock RPM muffler 2 1/4" in and out, slightly modified stock carb from Todd (rebuilt), electric fuel pump (35 gpm @ 4-7 psi), stock distributor (centrifical advance seems to be working but the vacuum does not appear to do much) (advance at 800 rpm is 8 deg, 3000 rpm is about 25 degand it keeps going up but slower), 92 octane gas. Vacuum in manifold under unloaded acceleration is near 20 in/hg. I have all the vacuum hose ports on the carb attached to themselves using short lengths of hoses. The only things coming off are the hose to the break booster from the side of the manifold, the PCV hose from the big hole at the back/bottom of the manifold, and an adjacent line to the distributor.

By Zippy (Zippy) (152.163.213.81) on Monday, June 18, 2001 - 03:02 pm:

I have some hypotheses on what the problem could be.
(a) low fuel volume/pressure
(b) bad spark (faulty coil) (i did a check on it with my ammeter and it appeared to be ok but I don't know it this could cause this problem)
(c) funky jetting??
(d) my carb does not have an air filter on it yet. When I floor it with out a load, some fuel and air seems to come out the top (like the air that moves in the wrong direction near a fan).
(e)excessive crank case vacuum (roughly 5 in/hg)

I have some thoughts of what it can't be
(a)head timing (seems good)
(b)points, plugs, condenser, cap, rotor, wires (new)
(c)fuel quality (cleaned tank, new gas)
(d)ignition timing (covered)
(e)valves (just did the head)
(f)distributor shaft (good dwell)

This car is killing me financially. I can't afford to just randomly throw $$ at it right now. My wife is at her limit.

Thank you for any assistance / ideas / etc.

Roger

P.S. Thank you for your advice re: 10" tires.

By errol (205.188.195.183) on Monday, June 18, 2001 - 09:33 pm:

Get a new wife, Preferably younger... only kidding. Look at the coil wires, if they are 'wrapped' around the top of the coil. if they are, unwrap them.
Take the vacume advance can off and squeeze it in a vise just a little to get alittle more advance. (or just take a vacume gauge/pump to see when the advance kicks in. you should be all in around 2200-3000 rpms depending on your gears and tourque the engine is producing.
I know this sounds foolish but use a cooler plug..or just look at them and see which plugs look like what. ie. oily, sooty, burnt, If you don't have a good coil you don't want to have a big plug gap. And scrape off the deposits on each inside terminal of the cap. and smear a 'small' amount of dialectric grease on the rotor and contacts.
looking at what you wrote again makes me think it's your vacume advance on the distributor

By Adrian (Civicguru) (203.42.97.227) on Monday, June 18, 2001 - 09:51 pm:

I would have said fuel (faulty pump or carb not jetted right), though the ignition breaking down could also be the problem. In any case, I'd ditch the standard carb if possible as they aren't that great and only good for upto about 80hp or so.

By Zippy (Zippy) (205.188.193.158) on Tuesday, June 19, 2001 - 05:12 pm:

OK. I did some looking. The plugs are lightly black (about 1.5 hours on engine) and I interpret them as indicating that I have a rich mix, which would be consistant with an electrical problem causing poor combustion (especially since the last half hour on the motor was at the parking lot trying to make the car go fast). Do you agree with this interpretation??

I checked the vacuum advance on the distributor and I have questions. My car is a '79 but on the distributor I have 2 locations to plug in vacuum lines, one inner and one outer. The outer plug will hold a vacuum but the inner plug will not show a vacuum, air just seems to rush through. Is this a distributor from a model with a vacuum retard and advance?? If so, is the vacuum setup I described normal?? Let me tell you the procedure I used to check the vacuum advance and see what you think. I have a hand held vacuum pump (it moves my THOP at about 5 in/hg) and I plugged it in to the outer plug on the distributor with the car idling. I pumped the vacuum to about 25 in/hg and the timing advance did not change any. I then put the pump on the inner plug and pumped it as rapidly as I could and nothing happened (no vacuum was sustained and no advance occurred). As I said earlier, the centrifical advance is OK. Can this vacuum advance issue be causing my problem. If yes, is this conclusive??

Please don't focus on the distributor issue to the exclusion of other hypotheses but any advice on a distributor would be appreciated. Can I do an effective rebuild on the distributor vacuum system or should I just buy a new one? If I have to buy a new one would this be a good time to upgrade to an electronic ignition (god that sounds expensive)?????

Thanks,

Roger

By Todd (63.52.20.118) on Wednesday, June 20, 2001 - 12:44 pm:

Hey Roger,
How does the car run before it gets to 4000 rpm? Are you still using the stock cam? The 25 degrees and rising from 3000 sounds a bit peculiar. You should be at full advance by then. If your vac advance isn't working properly, it would give it less advance which would cause it to run better at higher rpm. Sounds like at least one of the vacuum chambers is shot so make sure that one isn't hooked up causing a vac. leak. With the symptoms you describe, it sounds like your cam is advanced too much, but you said that part is good.
As far as your plug readings go, you either have a rich mix or bad ignition. This is assuming you ran the car at the rpm where the problem is and cut it clean.

By Zippy (Zippy) (205.188.197.41) on Wednesday, June 20, 2001 - 02:46 pm:

Thanks Todd,

The car is very strong until it cuts out. Yes, I still have the stock cam. As far as the ignition timing goes, please explain why it sounds peculiar. It rises in a vaguely linear fashion until about 3000 rpm and about 25 degrees. I think it continues to rise up through 4000 and possibly 5000 rpm but it is still a fair amount below about 30 degrees by then. No vacuum advance should help with high RPM power???? Please explain this. Yes, I've been using the chamber that maintains a vacuum so there is no intake leak. I'll try putting the cam back a notch and see if I messed it up somehow. Do I or do I not need to do somthing about my distributor?

Roger

By Nikolaj (213.197.4.72) on Wednesday, June 20, 2001 - 09:10 pm:

I have had good experience with driving with a faulty hose for the vacuum advance. This is what happens, basically... The car will run fine from somewhere around 3000, but when stopping, it will die unless you keep the gas on it. But then again, I guess if the advance is stuck, you could have that problem on the other side of your tach, but you say it does move. It doesn't sound like that's the problem.

By errol (152.163.194.176) on Thursday, June 21, 2001 - 09:21 pm:

Zippy; do one thing at a time. Get yourself a new vacume advance can. (one that is just a single ported one, or just a 'advance' with no retard. They are easy to change!! Next, after you get that taken care of, look at your plugs again. Are they still 'black'? If they are it might be a small diaphram on the underside of the carb that will just piss fuel in the venturi if it is bad. But if it is it won't run good at all either. I know it takes time to do a trial and error but you can drive yourself nuts (like me) chasing down two or three different things. Oh, and clean those plugs every time you pull them out. (you'le get good at it and intimate!) A good 'Spiral core' ignition wire will help also. errol

By Zippy (Zippy) (64.12.102.51) on Friday, June 22, 2001 - 07:37 am:

Thank you all so much. You have been very helpful. Whenever I dig in to a new part, I build it up in my head like it is some great puzzle. Well I opened up the distributor last night and did a rebuild. Well, it's pretty much worn out. The counter-weight advance parts are grooved and do not move smoothly which accounts for the late advance I discussed above. The parts allowing the vacuum advance were jammed tight. I loosened them up so that they operate freely now but I don't have a working vacuum can. So, I guess I'll start with a new distributor (it seems I need one). If that dosen't do it I'll hot wire the car and see if that helps (mabye there is a voltage drain or somthing between the coil and battery). If that dosen't do it I'll get an Acell coil. If that dosen't do it I'll change back to my old carb. At some point in there I'll move my head timing around a notch in each direction. If none of these do it then mabye me and zippy will take up flying instead of autocross .

Roger

By Todd (63.52.3.51) on Friday, June 22, 2001 - 10:14 am:

Don't give up Roger. I know how frustrating it can be to spend all that money and time on a car only to have a gremlin like this show up. Makes you feel like driving it off a cliff. It'll show itself eventually.

By Zippy (Zippy) (205.188.196.48) on Saturday, June 23, 2001 - 04:41 pm:

I took out my dremmel and went to work on my distributor weights in an attempt to make them run smoothly. It helped. The advance in now running much smoother but was no help to the big problem. Hot wired the coil, no help. Adjusted my valve lash. It was set at 0.008 and now it's at 0.004. No Help. Played with my head timing, no help. Changed the carb and it appears to have helped. The only trouble is that I have no plates or insurance and if I want to test it I have to tow it to an empty parking lot. So... I'll find out tomorrow how it is behaving.

Todd, in a previous thread you mentioned the name of a site that had a great deal of tuning info. I hunted the threads but could not find it. Would you repeat it for me?

Thank you Richard for the site and all the users for your moral support.

Hey, I live in PA, near Philly. Does anybody else live in the north east? What racing club are you in?

Roger