Dieseling/run on

[bugedd]

My 1275 has been experiencing run on lately, but not all the time. It starts and runs seeemingly fine. I just fired the car up with the 40DCOE for the first time this morning, with the jets dialed just about all the way in, ran it for a bit, and it backfired a few times and then dieseled when I shut it down. It also did this with the Weber DGV that was on it.
Now, would this likely be a timing issue, such as too much timing? I had set it once when I first got the car a couple years ago, so perhaps something has changed? And what is the optimum timing?
Any other possible causes?

 

[aeronca65t]

Idle speed too high?

Sometimes, with bigger carbs, this can be tough to fix, since the engine may not idle nice and low (say around 700 rpm or less) as it would with SUs.

 

[Jim_Gruber]

It takes Premium Gas. If you aren't using Premium there is a good chunk of your problems. When these engines were developed gas had one heck of a lot more octane 40-50 years ago.If I run even Shell 93 in Bugsy my 1098 I have issues with dieseling if timing is too far advanced.

 

[tomshobby]

Idle speed too high?

Sometimes, with bigger carbs, this can be tough to fix, since the engine may not idle nice and low (say around 700 rpm or less) as it would with SUs.

x2

 

[Guest]

Idle speed too high?

x2

X3 check timing too.

It can rn on two ways: first is a chamber too hot (timing too advanced) and idle speed too high. It will keep trying to run on if the idle circuit will syphon. Second way is it'll run backwards. It's just like before but the motor will kick back and run off of the unburnt a/f mix it just pumped into the exhaust when you cut the key.

 

[Westfield_XI]

Kellysguy, great explanation of how a motor will run backwards. I suppose it was obvious to everyone else, but that really made a light go on for me. Thanks.

 

[Guest]

Kellysguy, great explanation of how a motor will run backwards. I suppose it was obvious to everyone else, but that really made a light go on for me. Thanks.

Don't feel bad, took me a while too.

 

[bugedd]

Never knew about the premium gas, I've always used the 87 octane. I'll use the 91 from now on. And the idle is a bit high, about 1100. IT seems that it needs to be about 900 or so before the generator light turns off. Does that sound about right?

I'll mess with the idle this weekend when I get a bit of time and double check the timing. Any suggestions where that should be, or go by what the book says?

 

[JPSmit]

I use premium too, not just for the octane but also no ethanol.

Haynes says: Sprite Mk 1 - 5 deg BTDC

keep us posted!

 

[Guest]

I use premium too, not just for the octane but also no ethanol.

Haynes says: Sprite Mk 1 - 5 deg BTDC

keep us posted!

JP, you'd probabaly do better w/ 87 in a low compression motor. You still @ 7.5 right?

 

[Guest]

Never knew about the premium gas

Higher grades are harder to light and help combat this. Your head may have been shaved which will help comtribute with the above mentioned conditions.

 

[JPSmit]

I use premium too, not just for the octane but also no ethanol.

Haynes says: Sprite Mk 1 - 5 deg BTDC

keep us posted!

JP, you'd probabaly do better w/ 87 in a low compression motor. You still @ 7.5 right?

The only fuel I use is Shell V-Power which is 91 octane. It is the only one where the pump says "no ethanol." When I was using regular (87) I was having no end of problems - real gas made it go away.

BTW I just read this week (maybe even here) that the original timing marks are for 60's and 70's gas and that we should dial it further back a few degrees.

And, yes Billy, still 7.5

 

[glemon]

x4 on the idle speed, also more likely to happen if the car is running hot, of course there are lots of reasons for running hot, the most simple to adjust are usually mixture and timing.

 

[nomad]

The only fuel I use is Shell V-Power which is 91 octane. It is the only one where the pump says "no ethanol." When I was using regular (87) I was having no end of problems - real gas made it go away.

[/quote]

JP;
As a long time proponant of ethanol blended gas who has used it in Brit cars since the 80's, I'm wondering what problems you were having?
In these parts its the cheapest high octane gas you can buy and the only problems I've had with it are, I believe, vapor lock in hot wheather.

Kurt.

 

[RickB]

My Midget gets 10% less mpg on 10% ethanol.
If nothing else it makes for easy math when pure gas only costs 10% more.

 

[JPSmit]

The only fuel I use is Shell V-Power which is 91 octane. It is the only one where the pump says "no ethanol." When I was using regular (87) I was having no end of problems - real gas made it go away.

JP;
As a long time proponant of ethanol blended gas who has used it in Brit cars since the 80's, I'm wondering what problems you were having?
In these parts its the cheapest high octane gas you can buy and the only problems I've had with it are, I believe, vapor lock in hot wheather.

Kurt. [/quote]

Mostly vapour lock as you mentioned - starting when hot. Generally though (and it may just be me) it seems happier and revier and peppier with the straight gas.

 

[bugedd]

The Haynes MK1 spec is 5*, however its a 1275 motor that has the smog head. So do I still set at 5 degrees, or use another spec?

A couple things I noticed when I got the DCOE on the car is that it revs and snaps much better than it did with the DGV, which would imply the DGV was running pretty fat. The DGV would also leave black coming out the tail end onto the driveway. Also, the car warmed up much faster, surprisingly so actually. I guess that also would imply that the DGV was running fat and the DCOE may be too lean. I'll run it again tomorrow, lower the idle with a bigger return spring to overcome a little drag in the cable, set the timing to whatever it should be, then check the plugs.

 

[RickB]

I also notice a bit more pep and the car seems to run "happier" on pure gas.
This seems subjective measurement entirely judged by the seat of my pants.

What I can say is fact is that when I drove cross country last summer I got more miles per each tank when I filled with the high test pure gas than I did when I filled with blended gas and ethanol.

Some stations didn't have a choice, all I could get was blended.
When I had the choice I always chose the pure gas, mainly because I needed less gallons that way.

 

[nomad]

Guess we're redirecting the topic with this but since the alcohol molecule has less energy a little less MPG would stand to reason. I always figured price offset that.

Kurt.

 

[RickB]

Right, it's about equal mpg / price. That turns out to be a wash, so it neither costs more to use pure nor does it cost less to use blend.

So the benefits of using pure gas are:

you use less total fuel

have to fill up less often

no worries about alcohol damaging anything in your old car fuel system
(if you worry about that kind of thing)

subjectively feel a little more zing
(subjective opinion, but there is greater energy density in gasoline than in alcohol so it seems to have some basis)


Benefits of using gas with Ethanol?

It's more readily available everywhere
Corn farmers get to sell corn for higher prices?
Cattle farmers look to other crops to feed cattle or pay the higher amount for corn? Or grow your own?
(Kurt I know that has to hit close to home, so what's your take on it?)