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Loss in top end power

Posted: Thu Apr 11, 2019 12:53 pm
by mngreen
What would be the most likely suspected problem in a T that recently had a noticeable loss in top end power under load going up hills? This was not previously a problem. Stock setup, no fuel filters, Holley NH carb. The engine sounds good and smooth but simply seems to slow down at top end. :roll:

Dirty plugs? Clogged carb jet? Dirty/blocked needle valve? Slipping high speed clutch or weak spring? Crap gas? Loss in compression?

Re: Loss in top end power

Posted: Thu Apr 11, 2019 5:29 pm
by John.Zibell
If engine RPM is dropping, it isn't the high speed clutch. All the other items you mentioned are still possible. First I'd check for adequate fuel flow to the carb and proceed from there.

Re: Loss in top end power

Posted: Thu Apr 11, 2019 6:18 pm
by John kuehn
How much gas in the tank? Stopped up vent hole in gas cap? First thing that comes to mind would be fuel starvation somewhere.

Re: Loss in top end power

Posted: Thu Apr 11, 2019 6:31 pm
by Scott_Conger
Three questions:

So, going up hills has never been a problem before?

Is it hotter than normal at the top of the hill?

what work have you recently performed?

Re: Loss in top end power

Posted: Thu Apr 11, 2019 6:56 pm
by Charlie B in N.J.
Good suggestions and questions so far. I'm assuming you're using the spark lever correctly.

Re: Loss in top end power

Posted: Fri Apr 12, 2019 9:37 am
by mngreen
No problem with this particular hill before, only had an additional passenger, so not a lot of added load. The problem seems to have been getting up enough speed to get a jump start on the long hill. This hill is near my house so it is not new and I have always been able to get a good running start to crest it, but not recently. Spark lever used properly, only general maintenance work done recently such as greasing the u-joint & other grease cups. I never let the gas level in the tank get below 1/4 full. I did tighten the low band a quarter turn for wear, but I have done this previously over time with no ill effect with no added drag. If it was fuel starvation (or clogged vent in cap), why would the engine have no problem in low band at high revs at the crest of the hill when it bogged down in high?

I am thinking more about cleaning the plugs (they are new Champion X), which I have not done in over a year, flushing out the carb bowl and checking the needle valve this weekend. I will also double check the gas cap for venting. I do know that I am really due for new rings (getting smoke), but have been delaying that by putting in Restore in the oil at twice annual oil changes for the past few years.

Re: Loss in top end power

Posted: Fri Apr 12, 2019 9:55 am
by Charlie B in N.J.
Sounds like your on the right path as far as checking things goes. I might add a wet/dry compression test just for the added info concerning and smoke/low power.

Re: Loss in top end power

Posted: Fri Apr 12, 2019 10:14 am
by Scott_Conger
Don't kid yourself. One extra passenger on a hard hill is a big deal. If you can still take the hill by yourself, you have nothing to fix. If it bogs down with just you, then you have something to work on.

Re: Loss in top end power

Posted: Sat Apr 13, 2019 8:52 am
by Adam
My first thought when I read the post was that the car weighed more!

Re: Loss in top end power

Posted: Sat Apr 13, 2019 5:34 pm
by mngreen
No fuel issues found. Pulled & cleaned the plugs--very sooty and dirty! Compression is relatively low ~45-45-35-35. New rings & valves are probably overdue.

Went to fill up fuel and pulled the hill, no problem!

Problem is......the extra passenger was my wife! :mrgreen:

Re: Loss in top end power

Posted: Sat Apr 13, 2019 5:48 pm
by Dallas Landers
Mike, I think I would put some money into making that T a real horsepower machine rather than tell the wife!

Re: Loss in top end power

Posted: Sat Apr 13, 2019 5:49 pm
by RajoRacer
Compression not too bad but "--very sooty and dirty" plugs sounds as though you might be running a bit on the rich side - try leaning her out a bit - your carburetor, not the wife !

Re: Loss in top end power

Posted: Sun Apr 14, 2019 9:56 am
by George Mills
I'd fully agree with Scott...there is only so much you can do with a 20HP machine. Playing experiments to get it to 24-25 HP equivalent is not going to change much either...its' the nature of the beast, something about HP difference needing to be squared while the load change is linear...

I'd say reported compression works...#3 is at the low end and some hold that compression should be within a few pounds, but where you are at would not bother me for now.

The soot mentioned is probably as pointed out the lean/rich setting and maybe you can ask for advice here...everybody has a different way to do it. Simple answer is it you go too far in the lean direction, the thermo-gurgle cooling system will let you know...quick.

Sounds also that you might benefit from approaching hills in a different way? I'm not sure you have fully explained your method. While it helps to roll a bit into a hill with some speed, do you modify the spark at any time on a routine hill climb? If you know someone local with a sedan body ride with them on that hill and others. My guess is that the sedan guy has to use this two stick method to take on the hill and you will see what I mean. Sometimes if it labors, due to load, due to whatever, you may need to use the clutch too low...

I'd suggest you try some of these ideas before you believe you need to tear into things. Eliminate the obvious...only then go from there

Re: Loss in top end power

Posted: Sun Apr 14, 2019 10:19 am
by Adam
10 pounds low on the rear 2 cylinders is a balance issue that in itself consumes a little power. Also 35 pounds is darn low. A fresh engine is 60 pounds. If you do rings and valves, and get your cylinders close to 60 you will have a noticeable power increase.

I’m not saying this will work, but you might want to try an experiment that won’t hurt anything... Put 4oz of Marvel Mystery Oil in your engine oil, and add some to your gasoline according to the bottle directions. Run out a whole tank of “treated” gas (at least 8 gallons). Then re-test compression and post your results here. It won’t fix anything “mechanical”, but occasionally may improve “sticky” ring and valve issues that are a product of extended periods of storage, etc. The only reason I mention this is because it is the very beginning of the driving season...

Re: Loss in top end power

Posted: Mon Apr 15, 2019 12:24 pm
by mngreen
Thanks Adam, I usually run MMO in the gas at each fill up. In fact, I purposefully did NOT add MMO for this last tankful, in case the MMO was diluting the gas too much for the hill :roll: .

I have never added MMO in the oil for fear that the 5W-30 that I use would get too slick for the bands :geek:

Gonarunit till it runs nomo... :idea: