Stupid Question Dwell vs Gap

[Mahoney]

I am of the understanding this is the same thing, only measured differently? The gap is the space between the points when the ignition rotor is on its apex/corner. Dwell is the degrees before hitting that apex the points begin to open? I am a little confused. I am having some issues with having my engine run at idle of 500-650. It will only run smooth at around 1000 and above and sounds great doing it.<br /><br />I have ordered a new float and rebuild kit for my carb, but was wondering if I might be missing something in the ignition system.

 

[Don S]

Re: Stupid Question Dwell vs Gap

Dwell and gap do the same thing. I use gap as a preliminary to check the dwell. The dwell angle is much more accurate.<br />Your carb problem may be plugged passages in the carb. If water gets into the carb and is allowed to stay for any length of time, it can cause corrosion that will plug up the passages. Sometimes permanetly.<br />You might also try putting a vacuum gauge on your engine and seeing if you have a vacuum leak somewhere. The vac leak would also cause your idle problem.

 

[Boomyal]

Re: Stupid Question Dwell vs Gap

Mahoney, forget about the confusion between dwell and gap. Forget about the need to adjust same. Get a pertronix II igniter and the issue will become moot.

 

[Mahoney]

Re: Stupid Question Dwell vs Gap

haha, this is a gift boat, and a fairly nice one 1974 Cobalt with 225 v8, so not looking to spend a lot of money on it. The carb was sitting with water in it for a long time, and I took it off and cleaned it quickly and reassembled. it was my first time, I like tinkering with things. When the new float and rebuild kit get here I will take my time with the solvents and compressor and make sure I do it right.<br /><br />What is really involved with testing the vacuum on this 1974 225 GM OMC?

 

[KaGee]

Re: Stupid Question Dwell vs Gap

Originally posted by Boomyal:<br /> Mahoney, forget about the confusion between dwell and gap. Forget about the need to adjust same. Get a pertronix II igniter and the issue will become moot.

Pertronix does not make one for mine! <br />(3.8L w/Prestolite Dist)<br /><br />Dwell can be off a little and the engine will still run ok. Actually, I think the problem may be reverse if it were dwell... i.e. will idle, coughs when accelerating. <br /><br />The gap method can be a pain sometimes, I prefer the dwell meter.

 

[dick]

Re: Stupid Question Dwell vs Gap

And after you set the dwell don't forget to check the timing.

 

[Mahoney]

Re: Stupid Question Dwell vs Gap

Timing seems good, however I can't get it to idle slow enough to set it to 10o BTDC at 650 rpm, so I run it at 1000 and check the advance and listen to the engine, at about 1000 rpm, timing light is indicating roughly 15-18 degrees advance. Engine sounds pretty good at this speed however it still surges as it occilates between 950 and 1100 rpm, so I am thinking it is definitely a carb problem.

 

[Sharps-Nut]

Re: Stupid Question Dwell vs Gap

Dwell is more accurate than gaping with feeler gauge, both work. The thing that gets some people in trouble is gapping used point with a slight *** burned on them with the feller gauge method, the *** causes the gap to be off. Just my experience selling parts and fixing problems that come in over the counter. Your results may vary.

 

[jlinder]

Re: Stupid Question Dwell vs Gap

I recently had a similar problem where I had to have the spark advanced a lot to get a smooth running engine. Had carb rebuilt and timing is back to normal.<br /><br />Have you also looked at a general tune up? (Points, condenser, dist. cap, wires, spark plugs)<br /><br />With a boat that sat for that long of a time it would seem natural that a tune up would have been your first order of business, but you don't mention it specifically.<br /><br />Also, take a look at the plugs after you have run for a while. Amazing what you can find out by looking at the color of the insulator.

 

[Mahoney]

Re: Stupid Question Dwell vs Gap

I did not do a full tune up, although I did replace the plugs and gap them correctly, the boat was running great prior to storage, and when I took the distributor cap off, everything looked great, no corrosion, condensation, etc. Engine starts great, no hesitation whatsoever. Which is why I was leaning towards carb issues before I go spending money elsewere.

 

[Mahoney]

Re: Stupid Question Dwell vs Gap

Oh and plugs look dark colored(sooty), dry and even from ignition. Which I believe is normal.

 

[rattana]

Re: Stupid Question Dwell vs Gap

Have you checked the idle mixture screws. That will have an effect on your idle.

 

[Mahoney]

Re: Stupid Question Dwell vs Gap

Yup, been there done that, idle screws do make a little difference, but I have to have them almost all the way backed out for it to run its smoothest, further indicating more thourough carb cleaning rebuild is necessary. From everything I have heard they should be adjusted from a starting point of 1 1/2 turns out and I am WAY beyond that.

 

[rattana]

Re: Stupid Question Dwell vs Gap

Yep sounds like the carb needs to be cleaned and rebuilt.