acmoc

ACMOC Membership Benefits

  • FREE quarterly magazine filled with content about antique Caterpillar machines
  • FREE classified listings
  • ACMOC store discounts and specials
  • Full Bulletin Board Access
    • Marketplace (For Sale/Wanted)
    • Technical Library
    • Post attachments

$44 /year ELECTRONIC

$60 /year USA

$77 /year International

D7 3T pony motor not starting

More
10 months 4 weeks ago - 10 months 4 weeks ago #248458 by Fat Dan
It is going to be something simple when you find the problem, you watch.
If you are covering the throat of the carb that acts as a choke. If the carb is supplemented at high speed by the low speed jet. If the pony only starts and runs with you covering the throat of the carb or will not run without some or all choke. Most likely the LOW or idle SPEED CIRCUIT (jet and passages) are not allowing enough fuel by for the carb to operate correctly. Or the low pressure (vacuum from venturi(s) side of the Low Speed Circuit don't have enough vacuum to pull the correct amount of fuel air mixture. Gaskets, seals on the throttle and choke shafts, new o-rings, jets and seats help there. Super simple carbs here is a breakdown of a 955C D315 w/a down draft carb. See how the fuel pick up on this model pulls from the bottom.
A good set of Cat manual for your model are a must. First Cat tool I bought. 😉👍 op manual,,service manuals for chassis and engine(s) and a parts catalog for your serial number . Cat manuals only.
 
Good luck

ACMOC Member
955E 12A08263; 955C 12A04040; 955C 12A03563.
1954 No.12 Diesel Motor Grader 8T14777.
1945 No.12 Diesel Motor Grader 9K9320
1944-46 Adams Model No. 311 Motor Grader
1943 IH T9 Bullgrader
Attachments:
Last edit: 10 months 4 weeks ago by Fat Dan. Reason: Clarity
The following user(s) said Thank You: seiscat

Please Log in or Create an account to join the conversation.

More
10 months 4 weeks ago #248460 by V14
Replied by V14 on topic D7 3T pony motor not starting
I'm sure it will be something simple, rebuilding the carb will probably fix the issue but I'll have to wait for the parts to arrive in the meantime I'm just glad I can get it running by hand choking and hope making a better gasket tomorrow may make it easier to get off the trailer. I have the manuals for the machine, parts, service, and operators. Still need to buy one for the CCU but I haven't gotten around to verifying which unit is on the machine dealing with this pony motor. I'll need to figure out the right brake and the slight water pump leak after its off the trailer. Hopefully there is enough packing left that I can just tighten the water pump and the brake is a minor adjustment but we shall see.
The following user(s) said Thank You: Fat Dan

Please Log in or Create an account to join the conversation.

More
10 months 4 weeks ago #248464 by trainzkid88
dont use any of those silicone gasket makers. they are often a WOFTAM. get some actual gasket paper. and dress the gaskets with a little grease or aviation no3 form a gasket.

the only gasket maker to use is loctite master gasket 515,518 or 510.

silicone based ones are problematic as the excess breaks off and blocks things like fine galleries and valves.
The following user(s) said Thank You: Fat Dan

Please Log in or Create an account to join the conversation.

More
10 months 3 weeks ago #248470 by V14
Replied by V14 on topic D7 3T pony motor not starting
Someone recommended that stuff to me or I would have just bought gasket material instead for much cheaper, figures it's not good stuff. I'll just try and use it again for the day and then once the rebuild kit arrives I'll have a good gasket.
The following user(s) said Thank You: Fat Dan

Please Log in or Create an account to join the conversation.

More
10 months 3 weeks ago #248484 by trainzkid88
if you find you cant just nip the gland up and stop the leak. (note the gland should weep just a little to lube and cool it a tiny drop every few minutes is fine) you can buy gland packing at any irrigation pump service and most industrial suppliers.
The following user(s) said Thank You: Fat Dan

Please Log in or Create an account to join the conversation.

More
10 months 3 weeks ago #248488 by rax200
This may help it's on the zenith k style carby. 

 
 

regards 

 

Daryl

1937 RD4 4G4368
1940 D4 7J3717
1942 D4 7J9915SP
1942 R4 6G2550SP
1944 D4 2T6584SP
1945 D4 2T8978SP
1946 D4 5T6271
1956 D4 7U37855
1954 DH226 S/N 89 Howard Tug
Attachments:
The following user(s) said Thank You: Fat Dan, Busso20

Please Log in or Create an account to join the conversation.

More
10 months 3 weeks ago #248489 by neil
Replied by neil on topic D7 3T pony motor not starting
Based on your symptoms, you either have an air leak or insufficient fuel flow (blocked jets/passages, float level too low, fuel bowl breather blocked - that last one is not always obvious to folks)

Cheers,
Neil

Pittsford, NY
The following user(s) said Thank You: Fat Dan

Please Log in or Create an account to join the conversation.

More
10 months 3 weeks ago #248490 by 8C 361
I believe the pony on my '39 D8 is the same as yours. The only way it would run is with the choke closed all the way. The choke plate had the little spring valve that opened to let air in. I would dump gas down the carb and it would start and run good enough to start the main. I had taken it off to try to fix it. I could not find anything plugged up or otherwise wrong with it. While it was off my shop burned to the ground in the Oak wildfire and the carb was ruined. There seems to be heavy competition for any that come up for sale. saw a rebuilt one offered for $800. I found an imported knock off for $90, it is a good looking carb and looks like it willl fit right on. I have not installed it yet. If it works out I will post results on here.

Please Log in or Create an account to join the conversation.

More
10 months 3 weeks ago #248493 by V14
Replied by V14 on topic D7 3T pony motor not starting
I wouldn't be surprised if it was a blocked breather. Went to mess with it yesterday and while I was hand choking it I saw the fuel leaking out wasn't from badly made gasket, there was so much pressure it was seeping out of the idle adjustment screw. I ordered some tip cleaners someone else linked and the rebuild kit should be here early next week. I hope that will fix the issue and not need a new carb.
The following user(s) said Thank You: Fat Dan

Please Log in or Create an account to join the conversation.

More
10 months 3 weeks ago #248496 by neil
Replied by neil on topic D7 3T pony motor not starting
Sounds good - inappropriate "fixes" are often the cause of further issues : )

Cheers,
Neil

Pittsford, NY
The following user(s) said Thank You: Fat Dan

Please Log in or Create an account to join the conversation.

Time to create page: 0.438 seconds
Go to top