[>:]I'm as new as they get to this forum, and am needing some help. I have a 68 with a 400, msd ignition,race demon carb, I have no vaccum advance and no choke, I have set the timing to 8 btdc, idle at 1100 rpm and vaccum is 11hg and the engine is hot, it will disel when it is hot. cool it shuts down ok. i have no overflow on the rad it runs out , the coolent is about 3 " below filler neck.If this had a overflow would this help keep the engine cooler?

 

Make sure you have at least a 16 lb. radiator cap on it.Yes, put a over flow tank on it, and afan shroud, if you don't have one.

 

Pre-ignition of fuel is the most likely cause of your "diesel effect", very common when engine runs too hot and engine compartment is too hot also. If your gas lines/carb end up getting too hot you might then experience vapor lock where the gas turns to vapor prior to reaching the carb jets. Certainly the overflow, radiator cap,and fan shroud are excellent suggestions, you might also want to check your thermostat to see if it is working properly, a lower temp thermostat might also help. Larger radiator is also an option, not sure what is available in that arena. You may want to check and possibly re-adjust your timing, engine tune can contribute to higher temps as can a too lean carb mixture. I often ran my '69 Z/28 with no thermostat in thewarmer months as it always had a tendency to run hot (even brand new from the factory).
Clyde

 

What kind of other timing related issues are you having? knock, ping, detonation etc... I am also curious about what else has been done to the car?

 

as for timing problems there is no pinging,knocking or detination,step on it and it goes, brake hard and it doesn't stall out, I use 94 octane, I do have a fan shroud, new 16 rad cap new 160 thermostat,as for a lean fuel mixture I've adjusted the idle mixture screws in several postions, no success,should I try to rejet the carb?

 

A few things to consider.

If you are correct on your timing settings,it is not the problem unless your springs are so week it's causing too much mechanical advance. Set your total timing at around 3000-3500rpm and make sure that it is not advancing any more after those rpms. A good rule of thumb is around 8-14° initial timing and all in between 32-38° around 3000 rpm for autos. These numbers are for any decent "street rod" motor but can vary from car to car.

Re-jetting a few steps higher is not a bad idea. Jet far enough to make sure that's the culprit. Then begin to jet down 1 step at a time till you're where is runs the best. This WILL take more than a couple of tries if it is the problem.

If that 160° thermostat is a high flow, try putting in a normal flow thermostat. The coolant may not have enough time in the radiator to cool down before it gets cycled back to the engine. This is why many people put restrictors in the thermostat housing instead of a thermostat. It's more onslowing down/speeding upthe flow rather thantiming the temperature. Hopefully that last statement was clearer than MUD.

Did you have the engine rebuilt or did you buy the car that way? Do the heads and the block match. The early 400 blocks were notorious for getting hot so the later model blocks and heads had steam holes drilled/cast into them. If you get a block that doesn't have steam hole and your heads do, or the reverse, this will cause overheating problems as the water/steam has no where to circulate.

Remember that we're in the summer months too. Cars run hotter. 400's typically run hotter as well. With those tight siamese bores in the block, there is very little room for a water passage, hence it's harder to keep the block cool.

Where's your temp sending unit located anyway?

RM

 

ok Ithink I have solved the problems, here is what i found, the heads are from a 302 3927186 bock is a 400 3951509, I adjusted the carb to factory settings according to Demon,settings then adjusted the timing to 12 deg then adjusted the carb for the most vac 15Hg then tried to shut it down it would diesil a bit then adjusted the timing down 4 deg then readjusted the carb again, then it would hesitate as the gas was under hard accelleration, so then again adjusted timing to 10 deg readjusted carb, runs awsome, thentook out the plugs and cleaned and regapped the plugs once again rechecked timing and carb, all ok, as for the heating problem i do think the problem was do to timing and mis adjusted carb, I'm not exactly sure what the temp is as I just found out the guy i bought the car from must have taken the aftermarket gauges out but left all the wiring. Any ideas on what kind to buy? Thanx for your input guys it got me thinking differently about what was happening