HM100 hard starting.

Cuda54

Active Member
#1
My HM100 is hard starting when it is the first time. The first cold start take a while even choked once it is warm just a short pull and it fires right up. When it is running it idles fine and has good throttle response. But really hard to get it started the first time after it sets a while. It has a new plug and it has a lot of spark too. It has gas shut off but we turn it on and wait 5 to 10 min before trying to start it. I have had the bowel off and it is clean and we have taken the fuel line off and sprayed carb cleaner. Sprayed carb cleaner into where the jets are too. Thank GOD it has a electric start to get it started the first time. I need to get a battery wired in but thinking of putting in a 340 and I would have to rewire again. As the 340 does not need a battery to run the lights. This is on my TRI-ROD.
 

Cuda54

Active Member
#3
Yes and I have adjusted it and got it to run the best and idle where it is at. It does it only on the first cool start then it starts fine. But if it sets for a week on more is when it acts up.
 
#5
We have a 1974 Tecumseh HM80 on our Heald Super Bronc that was experiencing the EXACT same symptoms you are describing. It would take 6-7 pulls on the recoil in cooler weather on cold start. Just like yours, after the initail cold start the engine runs, idles, and performs perfectly. Also, on restart while still warm it will start on the first pull. Ours is a conventional pull start so it was even MORE bothersome than yours with the electric starter! We have got it to start in start in only 3 pulls now. Here is what we did to correct it:
On our engine I noticed that the choke plate had extra round vent hole, about 3/16" in diameter. We closed that off with a tiny stainless steel button head bolt,nut, and lock washer (also used blue Loctite). That allows a richer mixture when using the choke (less air). I know, kind of a "band aid" or "get-er-done" fix, but it works. I think part of the problem is that both the HM100 and the HM80 have that REALLY long, upward-curving intake manifold that creates a long travel distance for the fuel mixture from the carb to the combustion chamber
Michael
 

Cuda54

Active Member
#6
Regular gas but I will have to look at the carb again and see what it looks like. I might try a short reach pop rivet if that is what is the cause.
 
#9
Cold, non-vaporized fuel, with a long and torturous route. Extra-fat mixture gets to the plug sooner.
Few issues with this. How does the fuel become "non-vaporized"? The job of a carb is to properly atomize fuel. "long route"? So, why would long intake runner manifolds be used on this engine? "Extra-fat...gets to the plug sooner"? Please explain how mixture ratio impacts air/fuel velocity.
 
#10
Few issues with this. How does the fuel become "non-vaporized"? The job of a carb is to properly atomize fuel. "long route"? So, why would long intake runner manifolds be used on this engine? "Extra-fat...gets to the plug sooner"? Please explain how mixture ratio impacts air/fuel velocity.
Sloppily-worded, sorry.
A carb, especially the stone age ones on these engines, doesn't do all that great a job of "properly atomizing".
Long and bent intake allows/encourages droplets to build, falling from suspension.
Extra-fat, or rich, is what a choke/primer/squirt in the plug hole accomplishes. Quicker than unchoked/primed/squirted.
Getting combustible fuel in the spark's path is easier, when there's more of it, otherwise a richer mix wouldn't be needed for cold starts.
 
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