6r72 bad idle

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6r72 bad idle

Postby crosbyman » Fri May 18, 2018 5:16 pm

my beautyful 6hp won't repond to the LS needle adjustements yet runs ok above mid point but won't smooth down

Initially had my plug wires reversed...silly me :oops:

all the electricals have been redone time out with the voltmeter meter etc... all new wires , points etc plug booth etc... carb cleaned and rebuilt
I was rushed today so I did try running on one cyl then the other ...... to see if I had one cyl not firing causing the idle to fail

the in gear, high speed position purred nicely but seemed weak a bit for a 6hp it wasn't blazing away ( running on only cyl maybe??)

as soon has I hit he cottage i'll try for a retrest for good sparks on both plugs . compression was upper 70's 80'S

btw cheapy $27 OMC fuel pump on ebay worked nicely I could see it pumping gas on my clear line

any clues
IMG_1677.JPG (1.35 MiB) Viewed 258 times
6hp side pic.jpg
6hp side pic.jpg (93.15 KiB) Viewed 258 times
Last edited by crosbyman on Fri May 18, 2018 7:36 pm, edited 1 time in total.

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Location: Rhode Island

Re: 6r72 bad idle

Postby fleetwin » Fri May 18, 2018 5:28 pm

OK, well you will want to verify spark first...Couldn't really understand your explanation, except that you felt the engine was low on power in gear while running in the tank...It is surely possible that the engine is running on just one cylinder...
I'm trying to remember, is this engine new to you? Have you ever had it running before? If so, did it run OK then?
You say the engine does not respond at all to low speed needle adjustments, do I have it right? If so, perhaps someone has snapped the tip of the needle valve off, it is stuck in the mixing pocket, making the carb impossible to adjust...

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Joined: Tue Mar 10, 2015 11:39 pm
Location: Montreal Canada

Re: 6r72 bad idle

Postby crosbyman » Fri May 18, 2018 7:35 pm

good point.... on the bad. point i'll recheck

new to me motor purchased last nov-dec $60 as a winter project ... seized but I loosened it up

redid all electricals , carb ... come to think of it.... maybe I did not do the LS upper drip chamber ... but I do not recall the tip being broken off on inspection I 'll recheck that next time along with one possible dead cyl.

maybe one of my reconstructed booths was not properly seated on the plug tip

it is a real nice 6r72 it would be a shame if I can't get it to idle down

i'll update asap....

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Re: 6r72 bad idle

Postby BillW » Fri May 18, 2018 8:05 pm

If it was seized, you might want to start sweating the compression numbers...Over the years, I have found time and time again that I am only kidding myself, if I get one unstuck. It may end up spinning over but inevitably, the rings are still all stuck, not to mention cylinder wall condition. It may not be too bad if it started for you; but I'd still check....

Posts: 1034
Joined: Tue Mar 10, 2015 11:39 pm
Location: Montreal Canada

Re: 6r72 bad idle

Postby crosbyman » Sat May 19, 2018 12:04 am


I had the cyl. head off and cyl walls actually looked very good I think this motor just sat years and years in a back shop when the owner did not pick it up at a repair shop. my seized up 9.5 turned out pretty nice and made an excellent back up to my 75hp ETEC...

I used these less than 30 hrs / year

as soon as I can I'll tackle this 6r more closely ...winter isn't to good a time to put theory into practice

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