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Qjets rebuild as per cliffs book

S

slauder

Regular Contributor
"So other then my chainsaw, th

"So other then my chainsaw, this is my first carb rebuild. I’m using cliffs book for my decades of experience and wouldn’t be able to do the job without it (thanks cliff!). That said I am wondering how far to take it. I just got the idle tubes removed with punch, sheet rock screw and 30 seconds heat. They wouldn’t come off with either one alone. Looking at the spray carb cleaner it seems almost all acetone and wondering if I could just be using acetone alone as the cleaner? Also in my questions I’m not looking for better WOT but better GPH in all cases.

STANDARD
1. Throttle shafts: Cliff suggests to hone and insert bronze bushings. The modification stops a possible vacuum leak from the steel on aluminum wear. This modification is suggested only for primary shaft not secondary, but I see light thru the secondary shaft at casting when I hold it up to the light. Wouldn’t that cause a vacuum leak too? Also, is every one doing this as part of the rebuild? Wondering if I need to do this or if the marine application is creating less wear. I don’t have the bank of experience to draw a conclusion on.

2. I see both throttle plates open to 90 degrees (good) but the primary does NOT sit all the way closed. It stops just short of all the way tightly closed, because stop at the linkage. If I hold up to the light you can see around the primary plates. I didn’t see cliff address this. Seems I could grind the stop at linkage a tad to get a tighter close. This would be addressed after the bushings change (if doing) of course.


HIGH PERFORMANCE
1. Anyone alter the idle tube size, idle down channel, mixtures screw holes? Looking for better GPH not WOT.

2. Anyone removing primary booster rings (increasing jets)? Cliff sugests this for marine or tow applications. This doesnt seem to stop secondarys from kicking in does it? Looking for better GPH."
 
"Throttle shaft bushings: good

"Throttle shaft bushings: good practice but not always done. Necessary: if your idle is stable and consistent over the course of a few trips, you can probably omit this step. Just remember, the casting will wear given enough time. If you feel the secondary shaft needs to be bushed, there are a couple shops that can supply those.

The primaries won't seat unless you back off the idle screw as it usually holds the plates open. The critical measurement is how far above the transfer slot the bottom of the primary plate is. If the primary closes, you won't get enough airflow to maintain idle. The throttle plates' "registration" (what i call the process to get them centered in the bores) should only be necessary if the throttle shafts are disassembled.

The idle tube orifice size, the down channel brass plug and the mixture hole sizes are all idle functions. Any changes here become moot when the rpm exceeds 900-1000 rpm. Most BBC carbs could use a a minor increase in the idle tubes, the rest should be okay unless you have noted specific issues.

If you remove the primary booster venturi, you have to richen the jet, just to keep that mixture close to constant. If you cruise only on the primaries, you shouldn't have to make this mod. It's big purpose is to increase the primary side air flow so you don't have to get into the secondaries as soon.

In terms of economy, for idling, consider adding the idle bypass air mod. Takes more time getting the tools out to do it than their actual use. Cliff recommended 0.080" for BBC's. Adjust the vacuum break per the book to start. If the engine is rich after start up, increase the opening to lean it up some. For economy at cruise, you can start with a thorough inspection while operating. Make sure there's no fuel slosh/leak out thru the gasket due to operating angle. Make sure the airvalve spring is working (should work in concert with the vacuum break "unlocking" the air valve). You can also tune to power system in the primary with the spring assortment in Cliff's kit."
 
Got cliffs kit and looking to

Got cliffs kit and looking to re-assemble this weekend. I didn't take apart the main well blead tubes off the air horn (hoping not to have to). One is lose and can slide in and out of the collar that is partally exposed.

I guess I could tap sideways on collar to compress. Cliff didn't mention handling this part.

Also I don't understand what function the "sight tube" plays. Mine is nice and browned and too short.. Will replace but what does it do?
 
"Your "red" loctite co

"Your "red" loctite commpound will retain it. I'm a bit concerned that you have the collar exposed as I've never seen one in that state. Roe's book mentions driving them into the air horn more but as a racing mod. He declared them "not easy to move."

If the collar on the other side is flush with the gasket surface, you may be ok. If needed, I'm sure Cliff could provide a replacement. I'd be inclined to stake the area if the loctite isn't sufficient.

The sight tube is a safety device. If the main fuel pump diaphragm ruptures, the sight tube provides a "safe" path to dump the fuel. The fuel goes into the sight tube due to the second diaphragm that those marine pumps are required to have. Without it, the fuel would make its way into the crankcase and them into the bilge.

I bought a 50' roll when I replaced mine. If you want somme, I'll provide it at no net loss. You'll have to mmeasure though as I can't remember if you need 2' or 3' for an engine. I was at my boat today - still floating though several inches higher now than this morning - and the hatches are frozen and are likely to stay that way for another week. (not mmuch sun)"
 
"Scott:

I must apologize fo

"Scott:

I must apologize for my earlier post. You said main ir bleeds - I was thinking about the secondary air bleeds; the two inner (smaller) tubes that extend below the airhorn when it is removed.

The main air bleeds can be staked or loctite'd. The critical thing is that the orifice opening be maintained as the source of bleed air. In other words, you don't want any 'leaks' around the retainer."
 
"mark, link is the picture fro

"mark, link is the picture from top of airhorn.

closer look is that i dont have a collar. what i thought was collar was actually cast (i need headset with magnifier and light). looks like locktite should work. I think i should be able to get it without leaks.

PS I'm floating fine and with the 40 degree days getting longer its not long before a blackfish trip with soft bait will happen.

pss strange how the "south" has a couple feet more then long island NY.

http://www.flickr.com/photos/lauder/4369741702/sizes/l/"
 
You weren't trying to incl

You weren't trying to include the air bleed in the picture were you?

You can likely change that F hanger and get gain some economy too. I used the edelbrock stuff when I went thru mine.
 
"I'm trying to finish up t

"I'm trying to finish up the rebuild now. Question about the threads on the two torx screws in side the horn. Should we be using any locktite or similar? I'd hate two have one drop down into the engine.

Mark,
I'll take you up on the offer for sight tubing. I'll get a measure next weekend when I install the rebuilt carb and let you know details.

Thanks,
Scott"
 
"RE: "How can you see the

"RE: "How can you see the gap between the rotor and the cap contacts? Renewing both is part of the standard tuneup."

Was inverting the Cap and incerting the rotor in the worn track on cap. New cap and rotor replaced. The old ones didnt look to bad, but some carbon buildup. saw a thread about cleaning and using a flat file to remove the build up, keeping the surface flat. I decided to pass on that idea.

Also needed to regap the plugs. Inproper gap on all plugs... was too small not .45 which I addressed.

RE: "On the 'rich' idle, did you have any control with the mixture screws once the engine warmed up?"

Seems it takes the manifold quite a while to get warm. I was expecting full open choke after temp gauge hits 155 F. Good five or ten minutes after that before the spring was full lose to open choke all the way.

Once that occured I was able to play and adjust the idle screws. If they both were fully seated (CW), you could hear and see the gas pulling from main fuel nossle. I was able back off 1.5 turns and the nossles stopped distributing the gas.

At that time I checked the exhaust and it was clear with no unburnt gas. Great!

I didnt have time to let engine cool and start cold again. I was running out of time to pull ucooler and get to marine parts store before 6PM.

I will address the issue next weekend. Thanks for you help."
 
Sounds like progress....nothin

Sounds like progress....nothing like some high quality parts to help with a rebuild....

I'd guess you are happy with the idle mixture. Suggest you revisit it when the rest of the projects permit. Best to do the mmixture adjustment after a run to ensure the engine is fully up to temp. A vacuum gauge also helps to optimize the mixture. Biggest thing is to make sure the fuel is flowing from the idle ports and not the mains.

You can adjust the choke a bit leaner based on what you've described. The coil responds with the manifold temp and isn't "fast" in that respect. Make sure the housing (chimney) is in good shape and isn't binding on the rod. You just want the choke plate to be closed when the engine is cool. Each one is a bit different and some trials are in order. You can manually move the choke plate to see how sensitive a given setup is. You only want enough choke to get it started; very little is needed once she's up and running.
 
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