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Vanillagurilla
Samba Member
Joined: November 21, 2017
Posts: 1061
Location: California
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 Posted: Mon Dec 10, 2018 5:34 pm Post subject: Re: Performance engine popping and sputtering mostly when cold. |
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| tzepesh wrote: |
| I had the same problem, it drove me crazy. Until I installed the chokes and all problems disappeared. It need to be a bit richer at cold temperature, for a few minutes. |
Hpmx carbs dont have choke provisions, there cast out of the design. |
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oprn
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Joined: November 13, 2016
Posts: 12744
Location: Western Canada
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Max Welton
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Joined: May 19, 2003
Posts: 10697
Location: Black Forest, CO
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oprn
Samba Member
Joined: November 13, 2016
Posts: 12744
Location: Western Canada
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| Posted: Mon Dec 10, 2018 6:40 pm Post subject: Re: Performance engine popping and sputtering mostly when cold. |
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Mine either.
That was one of the deciding factors in ditching them. Otherwise they were working as good as any single barrel twin carb set could be expected to. |
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oprn
Samba Member
Joined: November 13, 2016
Posts: 12744
Location: Western Canada
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| Posted: Mon Dec 10, 2018 6:47 pm Post subject: Re: Performance engine popping and sputtering mostly when cold. |
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| Vanillagurilla wrote: |
| tzepesh wrote: |
| I had the same problem, it drove me crazy. Until I installed the chokes and all problems disappeared. It need to be a bit richer at cold temperature, for a few minutes. |
Hpmx carbs dont have choke provisions, there cast out of the design. |
I am not aware of any copy that does Chinese or American. Correct me if I am wrong though.
I think they could be added to some of the copies but it would not likely be worth the machining time. Kaddies on the other had should be do-able. |
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Max Welton
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Joined: May 19, 2003
Posts: 10697
Location: Black Forest, CO
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| Posted: Mon Dec 10, 2018 6:55 pm Post subject: Re: Performance engine popping and sputtering mostly when cold. |
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Now, I do know someone who attacked the cold-start issue from a different angle.
He had an electronic ignition system of some kind (Mallory?) that allowed for a small control in the cabin that he could adjust the timing on the fly. He would advance the timing a little to help get it started and then use it to hold a slightly high idle for a few minutes. After that he would dial the advance back to normal and drive off. Said it worked pretty good.
Max
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oprn
Samba Member
Joined: November 13, 2016
Posts: 12744
Location: Western Canada
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| Posted: Tue Dec 11, 2018 5:41 am Post subject: Re: Performance engine popping and sputtering mostly when cold. |
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Yes I could see that helping. The biggest issue with cold starting is that gas does not burn in a liquid state and cold gas does not evaporate fast enough to support combustion. You need larger volumes of it to get enough in a vapor state to fire in the cylinder. That makes the engine act like it is lean. Once the metal in the engine warms up there is enough heat to vaporize it very quickly.
I don't know if it's been tried but you could pre-heat the carb bowls. Might be a bit of a touchy thing...  |
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Max Welton
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Joined: May 19, 2003
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Location: Black Forest, CO
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AlteWagen
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Joined: February 23, 2007
Posts: 8503
Location: PNW
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oprn
Samba Member
Joined: November 13, 2016
Posts: 12744
Location: Western Canada
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| Posted: Tue Dec 11, 2018 11:47 am Post subject: Re: Performance engine popping and sputtering mostly when cold. |
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| No restrictive air boxes and filters is the wrong way to go. That would only effect the high rpm mixture. For starting it's the idle mixture that needs to be richer. |
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Max Welton
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Joined: May 19, 2003
Posts: 10697
Location: Black Forest, CO
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oprn
Samba Member
Joined: November 13, 2016
Posts: 12744
Location: Western Canada
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| Posted: Tue Dec 11, 2018 7:39 pm Post subject: Re: Performance engine popping and sputtering mostly when cold. |
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| AlteWagen wrote: |
| First gen HPMX had the internal choke assemblies, most leaked causing tuning issues so people are practically giving them away. |
Ah! So is that where the "If you have chokes they MUST be disabled and blocked off!" came from? Is it limited to just those carbs then? |
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Danwvw
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Joined: July 31, 2012
Posts: 8892
Location: Oregon Coast
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| Posted: Tue Dec 11, 2018 7:58 pm Post subject: Re: Performance engine popping and sputtering mostly when cold. |
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just increase the Idle jet size and check to see what the accelerator pump jets are. .50 or .55 is good on both!
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AlteWagen
Troll
Joined: February 23, 2007
Posts: 8503
Location: PNW
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| Posted: Tue Dec 11, 2018 11:30 pm Post subject: Re: Performance engine popping and sputtering mostly when cold. |
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| oprn wrote: |
| AlteWagen wrote: |
| First gen HPMX had the internal choke assemblies, most leaked causing tuning issues so people are practically giving them away. |
Ah! So is that where the "If you have chokes they MUST be disabled and blocked off!" came from? Is it limited to just those carbs then? |
Ive seen the first gen empi HPMX and the early no name ebay clone 'IDF' with the internal components in place and a block off plate externally. I think it is the rubber o rings the break down and start leaking under vacuum condition. second gen got a solid rod instead of the plunger assembly effectively solving the issue. My view is to just block them if you are not using to avoid any potential issues in the future.
I remember seeing the enrichment (internal w/cable arm assembly) available on single 40 Weber IDF from redline some time back but not sure about now.
Also the Solex/Kadron with electric chokes were available from empi not that long ago. Thought the type 4 kits were the last of the available stock and I no longer see them in the catalog.
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Zed999
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Joined: March 04, 2018
Posts: 1248
Location: UK
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| Posted: Wed Dec 12, 2018 2:28 am Post subject: Re: Performance engine popping and sputtering mostly when cold. |
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| oprn wrote: |
| No restrictive air boxes and filters is the wrong way to go. That would only effect the high rpm mixture. For starting it's the idle mixture that needs to be richer. |
Isn't limiting the air to make the mix richer how all those stock solex carbs do it? Granted they also increase the throttle. |
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oprn
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Joined: November 13, 2016
Posts: 12744
Location: Western Canada
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| Posted: Wed Dec 12, 2018 5:56 am Post subject: Re: Performance engine popping and sputtering mostly when cold. |
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| Zed999 wrote: |
| oprn wrote: |
| No restrictive air boxes and filters is the wrong way to go. That would only effect the high rpm mixture. For starting it's the idle mixture that needs to be richer. |
Isn't limiting the air to make the mix richer how all those stock solex carbs do it? Granted they also increase the throttle. |
Ah yes it is a very crude device. It closes of nearly ALL the air even at idle effecting every circuit in the carb. If left closed the engine would start and then flood out completely as the rpms increased from the main jet dumping huge amounts of fuel in the limited air stream especially if you were to drive off with the choke on. On the choke butterfly at the top type of carb there is a little diaphragm operated device that pulls that butterfly open part way as soon as the engine starts to prevent this. Face the Solex carb and look at the top near the choke shaft. It has 3 screws and a triangular cover.
The genius part about the Weber/Dellorto enrichment system is that it parallels the idle circuit and like the idle circuit it only effects the idle and transition stages. The main circuit is not effected with the choke on. No need for such a device!
This enrichment system also includes a jet for the liquid and an air correction jet so it is not only tunable but it adds air as well as fuel to give you the high idle! It's almost a carb all on it's own. |
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Zed999
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Joined: March 04, 2018
Posts: 1248
Location: UK
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| Posted: Wed Dec 12, 2018 6:22 am Post subject: Re: Performance engine popping and sputtering mostly when cold. |
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| I had this situation earlier this year. I tuned the idles as lean as I could for mpg and got down to 45's. Fine when warm but almost impossible to keep running when cold (if it started at all) with much popping and banging. Back up one size idle jets and it's fine even though it's around freezing here now. DRLA40's. So as others have already suggested, maybe the OP is just a little too lean on idles. |
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