# Honda HS70 Won't Restart When Warmed UP



## orangputeh (Nov 24, 2016)

i already took off carb and cleaned thoroughly , check float and needle valve etc. 

Starts easily one pull when cold and runs real smooth at idle , medium throttle , fast throttle , etc. Can run it for 15-20 minutes and runs fine. However , if I shut off , it will not restart. Almost but no cigar. It also backfires when almost starting and with air cover off one time it backfired with flame.

Once it is cool or left overnight it starts right up. Does this suggest valves need adjusting? This hs70 has the same type motor as the old 50 and 55. It does not have a OHV cover to take off. 

Could it be something else rather than valve adjustment? I put a new plug in and the gap is correct.


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## nwcove (Mar 2, 2015)

i would be thinking coil, but ......


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## orangputeh (Nov 24, 2016)

according to the Honda shop manual the valves appear that they can not be adjusted on this hs70 or the has50 models.

step 3 in the manual states; when the clearance is too large ; replace the valve or valve lifter.

when the clearance is too small ; lap the end of the valve stem with an oil stone.

if any members have experience with these specific models I would appreciate your input.


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## RedOctobyr (Mar 2, 2014)

Valve clearances not being adjustable sounds typical for me, for a flathead engine. The adjustability is typically provided by the OHV mechanism, having that rocker arm that can be tightened/loosened. On my flathead Tecumseh, whose clearance was too small, I had to grind the back of the valve stem, to increase the clearance. 



Can you check the valve clearances, at least? They were fairly easy to check on my Tecumseh, hopefully that's the case here. 



- Do you have an inline spark tester, to check whether you're still getting spark when hot? The backfiring makes me wonder about valve clearance (more specifically, a valve not fully closing once the engine gets hot), or possibly timing. 



- Are you getting a spark when you rest the plug against the engine, with it hot? Getting a spark that way doesn't guarantee you're still getting a spark under compression, since that makes a spark more difficult. 




- If the coil is weak, you could try making the plug gap smaller, so the spark can jump more easily. If it suddenly restarts when hot, then maybe the coil is too weak to jump the normal plug gap. This would just be a test. 



- Can you check compression when cold, and when hot? If it's lower when hot, then possibly a valve isn't closing fully once the engine heats up.


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## orangputeh (Nov 24, 2016)

RedOctobyr said:


> Valve clearances not being adjustable sounds typical for me, for a flathead engine. The adjustability is typically provided by the OHV mechanism, having that rocker arm that can be tightened/loosened. On my flathead Tecumseh, whose clearance was too small, I had to grind the back of the valve stem, to increase the clearance.
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This is great advice. I will try your steps.

Yes, at least you can check the clearances.It is a flat head. The cold compression is 90 pounds. In a little while when it is cool I'll check compression when hot. I'll also narrow the gap a little on plug. And try the other stuff before checking clearance in morning. 

I have a feeling you are right about the valves when hot since it is backfiring back thru carb when it is hot while trying to restart.

appreciate it very much,


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## orangputeh (Nov 24, 2016)

good spark either way. even narrowed the gap a little.

started up easily after it cooled for an hour or so and ran great. ran it for about 15 minutes and ran great at all rpm's. tried to restart and it took 3-4 pulls. it started but was running poorly and popping and backfiring for about 5-10 seconds and then ran great.

checked compression and it was actually 5 pounds higher. from 90 cold to 95 hot. can try again later. and can check valve clearance in morning.


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## orangputeh (Nov 24, 2016)

could it be that a valve is getting slightly stuck when hot? I got it running but it sounded like carp popping an backfiring for about 10 seconds and then ran great as before.

3 mornings in a row , starts right up and runs great. ran it 15-20 minutes and runs great. shut it down and it wont restart . after about an hour it will start.

if it ends up being the coil I will be SOL since Honda nor boats does not carry that coil anymore. I would have to find a match perhaps if another machine uses that particular coil or a parts machine.


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## tabora (Mar 1, 2017)

orangputeh said:


> if it ends up being the coil I will be SOL since Honda nor boats does not carry that coil anymore. I would have to find a match perhaps if another machine uses that particular coil or a parts machine.



These guys list one available for $65.35 redondo marine / hardware / power / ISP-VAR 4/14/03 HONDA PARTS 



These guys list it available for $80.68 https://www.bikebandit.com/oem-parts/detail/honda/30560-889-801/b2860092


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## RedOctobyr (Mar 2, 2014)

Will it restart using starting fluid? 



You said you still have spark. You seem to still have compression. That then leads to wondering about fuel. 



I've heard people talk about vapor-lock in carbs. One example, I think, is if a fuel line gets too close to the hot engine, causing fuel in the line to vaporize. Which can mess with your fuel supply. Disclaimer, I've only read about this in-passing, I've never had to deal with it myself. 



But as we all know, you need fuel, compression, and spark. If you have 2 of the 3, then try adding another fuel source, and see what happens. I'd probably try that with no choke, to avoid completely overdoing the fuel supply. 



You said you still have a good spark when hot, right? That would imply to me that the coil is OK. If the coil seems bad, and it's ~$70 for a part that will *hopefully* fix it, I would start to think about re-powering it. I've heard people talk about spraying suspect coils with inverted canned air (to get the liquid refrigerant), or something, to cool them off, as a troubleshooting step. Run until it stalls, spray the coil to cool it, then see if it will restart. 



I have a borrowed Briggs OHV-powered pressure washer that's hard to restart if I let it sit more than 5 minutes or so. Restart right away, and you're fine. Wait an hour, and you're fine. But wait 5-10 minutes, and your arm will just get tired. In this case, I believe it's due to the engine's automatic choke getting "confused". And maybe from some current jury-rigging of the throttle linkage, to help avoid problems from a governor that doesn't work, and wants to run wide-open constantly. But honestly, I haven't dug into it a whole lot. 



Is there any time aspect to your hot restart? Like shut down, wait 10 seconds, and restart is OK, but wait 5 minutes and you'll get nothing? Does it backfire out the exhaust, or intake/carb? 



You could remove the head and look at the valve seats. If you had a valve that was hanging, and staying wide-open, you'd feel the no-compression. And you actually gained compression when hot. But it might be possible for one to stay open a bit, I guess? Or maybe the valve seat itself is messed up/moving, if these have an inserted valve seat?


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## orangputeh (Nov 24, 2016)

RedOctobyr said:


> Will it restart using starting fluid?
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if i let it sit for an hour it will start right up and run fine. it will run and run as long as i want it too. I thought about the gas cap thing. After running for about 30 minutes , i shut it down and it will not restart no matter waht. starting fluid , or anything I do.

if i let it sit for only about 3o minutes , it will start but run real rough , kinda coughing , backfiring thru both the muffler and intake , but after about 15-20 seconds it will run great again.

I have never had this problem before. 

It will start with no problem if I let it cool off for about an hour. and just run and run as long as I want it to. If it was a bad gas cap , wouldn't it stall after awhile? anyway , thanks for all your help. if i ever figure it out , i'll report back and maybe help someone with a similar problem.


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## RedOctobyr (Mar 2, 2014)

Is there a fuel shutoff? Could you run the carb dry, so the engine dies, then try to restart it using starting fluid? I'm just wondering if it could be so fuel-rich somehow that it *won't* start. I admit, I'm grasping at straws. 



But you say you have fuel, spark, and compression. And your timing seems OK, at least, though you *could* check that (it's a pain to remove a flywheel, though). So I'm kinda stumped. 



Do you have an inline spark tester? It's harder to make a spark under compression, so just checking for spark by laying the plug against the engine block isn't a perfect test. You might simply have no spark, and need a coil (I'm not suggesting just go buy one, though, without better understanding the problem). A cooling-the-coil test might also help shed some light on this.


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## orangputeh (Nov 24, 2016)

RedOctobyr said:


> Is there a fuel shutoff? Could you run the carb dry, so the engine dies, then try to restart it using starting fluid? I'm just wondering if it could be so fuel-rich somehow that it *won't* start. I admit, I'm grasping at straws.
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I feel like a dummy but your questions about fuel delivery pointed me to the obvious....the gas cap......was not venting.....only partially. enough to keep the motor running as long as needed but if you shut it down it would not deliver enough gas to restart.

so we tried it with the loose cap or the cap off and now it restarts every time.

so always go with the simplest things first.......boy ....could have saved me a ton of time.

thanks again for all your help and advice.

the funny thing is , I have all the Honda shop manuals . even the manual for just the engines with an extensive troubleshooting section. The section on the "engine won't start" does not even mention the gas cap not venting . 

I should have known and tried this in the first place since this problem has come up before. Hopefully this thread will help someone else.


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## RedOctobyr (Mar 2, 2014)

I'm glad you found the problem! 



I confess your symptoms wouldn't have made me suspect a non-venting gas cap, since the engine could keep running indefinitely. If there's no fuel pump, then the carb is just gravity fed, and it doesn't know whether the engine is running or not, the bowl should be filling in either case. If anything, I would have suspected it would be *better* after shutting down for a few minutes, since a slowly-venting cap (not fully-plugged-up, admittedly) would slowly allow the bowl to refill while the engine was off. 



Just to be certain that the gas cap is definitely the problem, can you keep the gas cap tight, and run it until it's hot? Shut down, try to restart, confirm that it won't restart. Then loosen the cap, and try again, and it should now restart. 



That test would just help rule out that nothing else changed today, letting it restart more easily than normal. Again, please don't take this the wrong way, I hope you're right that it's an easy fix, with the gas cap! It's just that your symptoms sound odd to me, if it's just a partially-plugged gas cap. 



For instance, why didn't using starting fluid get it to restart when hot? With the fluid, you were providing your own fuel supply, so I would have expected it would run even without normal fuel delivery from the carb. Unless it was something like suddenly having *so* much fuel that it was way too rich, and couldn't fire, but I don't know how likely that is.


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## RIT333 (Feb 6, 2014)

I'm with you on your comments RedOctober. Doesn't seem like a non venting gas cap would be the "real" cause here, but if it really is, all the better. An easy/cheap fix.


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## orangputeh (Nov 24, 2016)

RedOctobyr said:


> I'm glad you found the problem!
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you may be right because it would not start again when i tried the starting fluid.

back to the drawing board. more testing.


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## RIT333 (Feb 6, 2014)

Sounds like possibly a coil that is failing when it gets heated up.


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## orangputeh (Nov 24, 2016)

RIT333 said:


> Sounds like possibly a coil that is failing when it gets heated up.


I was thinking that too as a neighbor had the same problem with a 724. It would start and run in the morning but if you shut it off it would not restart . we changed the coil and no more starting problems.

we checked the plug spark after the engine had been run and it appears the spark was the same as before when cold. also it restarts now when hot with the cap off. however that still begs the question why it would not restart with a splash of starting fluid before. we tried that several times without success.

I even thought maybe we flooded it so shut off key and pulled starter cord 10 times and retried with key on and still not start. If we let it cool off for 45- 1 hr or overnight , it would restart easily.

have to do some more testing. It is over 30 years old and could still be the coil. we only tried the cap off deal twice so that is not a good indication. it could be coincidence.


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## RIT333 (Feb 6, 2014)

orangputeh said:


> I even thought maybe we flooded it so shut off key and pulled starter cord 10 times and retried with key on and still not start.



When trying that, it is best to turn off the gas, take the chike off, AND remove the spark plug to clear a flooded condition. I always run a lighter near the spark plug hole and spark plug once I have removed it, but that procedure is probably not OSHA compliant !


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## orangputeh (Nov 24, 2016)

RIT333 said:


> When trying that, it is best to turn off the gas, take the chike off, AND remove the spark plug to clear a flooded condition. I always run a lighter near the spark plug hole and spark plug once I have removed it, but that procedure is probably not OSHA compliant !


with my luck I would end up a candidate for the Darwin Awards.....


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