Finally got the Mack Mag built!

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Lol my only question with the muffler cap on wouldn’t that richen the mixture? I figured by having it off it would be breathing better and leaning the mixture out a tad? And I have the same issues regardless if the cap is on or off, it still does the same thing. Also I just read on a post somewhere that the placement of the inline fuel filter can affect how the carb runs? Due to maneuvering my carb position and trying different carbs recently my fuel filter has ended up pretty close to the carb itself maybe 1-2” away from the carb do you think this may cause the issue?
 
Lol my only question with the muffler cap on wouldn’t that richen the mixture? I figured by having it off it would be breathing better and leaning the mixture out a tad? And I have the same issues regardless if the cap is on or off, it still does the same thing. Also I just read on a post somewhere that the placement of the inline fuel filter can affect how the carb runs? Due to maneuvering my carb position and trying different carbs recently my fuel filter has ended up pretty close to the carb itself maybe 1-2” away from the carb do you think this may cause the issue?
Throttle lag is a symptom of lean condition, but 4 stroking under load is a symptom of rich condition, so maybe that back pressure will help to even things out.
As you are describing the symptoms of two completely opposite conditions, I think the problem has to be elsewhere than just the carburetor jetting.

If you only try fitting the cap, not fitting the cap and then keeping it on while jetting the carb, maybe you're not seeing a true picture of what the cap can do for you.

As I said, the back pressure from the (fully assembled) stock muffler may be a bit restrictive so you can try modifying it a little bit, just to improve the flow but leaving some back pressure.

It shouldn't be this difficult to get the jetting done.


And no I don't think it can be the fuel filter.
Certainly, I don't see any reason why it shouldn't be close to the carburetor. The lower it is below the tank, the more pressure there is to flow fuel through it anyway.
 
Throttle lag is a symptom of lean condition, but 4 stroking under load is a symptom of rich condition, so maybe that back pressure will help to even things out.
As you are describing the symptoms of two completely opposite conditions, I think the problem has to be elsewhere than just the carburetor jetting.

If you only try fitting the cap, not fitting the cap and then keeping it on while jetting the carb, maybe you're not seeing a true picture of what the cap can do for you.

As I said, the back pressure from the (fully assembled) stock muffler may be a bit restrictive so you can try modifying it a little bit, just to improve the flow but leaving some back pressure.

It shouldn't be this difficult to get the jetting done.


And no I don't think it can be the fuel filter.
Certainly, I don't see any reason why it shouldn't be close to the carburetor. The lower it is below the tank, the more pressure there is to flow fuel through it anyway.
Alrighty I guess I’ll do some more testing when I get home. Back to the sweaty 100+ degree garage lol!
 
Alrighty I guess I’ll do some more testing when I get home. Back to the sweaty 100+ degree garage lol!
I (almost) know the feeling haha. I have a lovely cool cellar with my noisy power tools in it, but then I have to come upstairs and watch TV while I fit things to the bike. :p
 
I (almost) know the feeling haha. I have a lovely cool cellar with my noisy power tools in it, but then I have to come upstairs and watch TV while I fit things to the bike. :p
Welp I’m officially out of things to try... I put the cap back on her and ran her down the road. The bike ran slightly worse with the cap on but basically the same as before. Throttle lag on the low to mid range and some four stroking at WOT. I’m not too worried about the 4 stroking at WOT I just don’t understand the throttle lag and crappy throttle response it’s having. Just for peace of mind I moved the fuel filter so I could eliminate that from my hopes of being the problem. I just don’t know what else I can try. The only thing different I can think of on this motor, which ran great on my other bike, is the extended intake I put on to fit this frame.
 
Welp I’m officially out of things to try... I put the cap back on her and ran her down the road. The bike ran slightly worse with the cap on but basically the same as before. Throttle lag on the low to mid range and some four stroking at WOT. I’m not too worried about the 4 stroking at WOT I just don’t understand the throttle lag and crappy throttle response it’s having. Just for peace of mind I moved the fuel filter so I could eliminate that from my hopes of being the problem. I just don’t know what else I can try. The only thing different I can think of on this motor, which ran great on my other bike, is the extended intake I put on to fit this frame.
Which carb are you using at the moment?
Have you checked all seals? Idk if it would be that but it's something to look at. :/
 
Which carb are you using at the moment?
Have you checked all seals? Idk if it would be that but it's something to look at. :/
I was using the stock NT. I even went so far as to put a brand new NT on there and tried it and it did the same thing. I believe I can get the WOT jetting figured out myself in the end but right now I’m concerned with why it’s lagging so badly on throttle from idle to probably 3/4ish throttle. I can have it sitting idling and turn the throttle and it won’t respond until a second later. I can rev it real quick and by the time my hand is off the throttle is about when it revs up. The same happens while riding around at the lower rpms, the throttle just isn’t responsive like it should be and if I cruise at half throttle it’s 4 stroking the entire time
 
I was using the stock NT. I even went so far as to put a brand new NT on there and tried it and it did the same thing. I believe I can get the WOT jetting figured out myself in the end but right now I’m concerned with why it’s lagging so badly on throttle from idle to probably 3/4ish throttle. I can have it sitting idling and turn the throttle and it won’t respond until a second later. I can rev it real quick and by the time my hand is off the throttle is about when it revs up. The same happens while riding around at the lower rpms, the throttle just isn’t responsive like it should be and if I cruise at half throttle it’s 4 stroking the entire time
Well that has got me scratching my head too. :/ Such a weird contradiction of symptoms as throttle lag and four stroking. Is the hose intake deforming? Not that I have any idea what that would do but I am now just guessing at things you can look at and check for abnormality.
 
Well that has got me scratching my head too. :/ Such a weird contradiction of symptoms as throttle lag and four stroking. Is the hose intake deforming? Not that I have any idea what that would do but I am now just guessing at things you can look at and check for abnormality.
No deformation in the hose, I’m starting to wonder if it’s an air leak somewhere I can’t find. If I’m riding and pull the clutch the rpms don’t settle right away and take a while to come down. From idle revving has a slightly longer come down as well. I don’t know what else could be going on. Same issue 3 different carbs tried so the only thing left that I know to check would be an issue with my CDI or spark plug. Could anything on the exhaust end cause any of these symptoms?
 
No deformation in the hose, I’m starting to wonder if it’s an air leak somewhere I can’t find. If I’m riding and pull the clutch the rpms don’t settle right away and take a while to come down. From idle revving has a slightly longer come down as well. I don’t know what else could be going on. Same issue 3 different carbs tried so the only thing left that I know to check would be an issue with my CDI or spark plug. Could anything on the exhaust end cause any of these symptoms?
There's ignition/combustion things that could maybe be mistaken for four stroking.. Not throttle lag though. That one has to be lean condition.
Small jet, intake vacuum leak, foamed fuel, fuel inlet valve blockage, fuel line blockage, vacuum forming in tank.. That's the whole list as far as I can recall.
What jet sizes are you using now? And what brand?
 
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