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Morse Cable giving me the herky jerky
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oprn
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PostPosted: Fri Jun 04, 2021 5:27 am    Post subject: Re: Morse Cable giving me the herky jerky Reply with quote

Give us a picture of the carb linkage from the side so we can see the angles they are at when at rest and at 1/2 throttle. Ideally 1/2 throttle all angles should be 90 degrees with equal deviation both ways. That should give the most linear action as far as linkage is concerned. If the angle is too steep at idle it will give you a touchy throttle off the start. There was a picture posted recently showing exactly how it shouldn't be, I will copy it here if I find it.

Here is another thing that could help. Initially with 55 idle jets my AFR was in the 12/1 range and fuel mileage was poor. As I changed jets to get it closer and closer to the ideal 16 - 17/1 for maximum fuel economy I found that inadvertently the throttle response just off idle became tamer and tamer. So in conclusion it seems fat idle jets make for a touchy gas peddle too.

Found it. This angle is way too steep. If you have something that resembles this then small wonder it's touchy!

https://www.thesamba.com/vw/gallery/pix/2176162.jpg
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jimmyhoffa
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PostPosted: Fri Jun 04, 2021 6:06 am    Post subject: Re: Morse Cable giving me the herky jerky Reply with quote

Well I've got the front half if he's got the back! I don't have a picture of the carb linkage, but it's very simple. It's configured like the CB single carb linkage.

The pedal is an old Neal configured with the cable pull perch as low as possible (closest to the pivot) which should be the better option. It takes more pedal travel to move the cable a given amount. This is it with the extra spring hung on it for testing.

Image may have been reduced in size. Click image to view fullscreen.

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PostPosted: Fri Jun 04, 2021 8:03 am    Post subject: Re: Morse Cable giving me the herky jerky Reply with quote

Here's the carb linkage. Throw is about as good as it can get and still give us full throttle.

Image may have been reduced in size. Click image to view fullscreen.


Image may have been reduced in size. Click image to view fullscreen.

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skills@eurocarsplus wrote:
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that fucking thing looks like it drove through a J.C. Whitney catalogue and hit everything on the way out Laughing
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oprn
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PostPosted: Fri Jun 04, 2021 11:01 am    Post subject: Re: Morse Cable giving me the herky jerky Reply with quote

Ah! It's a single center mount! I see... well, fabricating a longer arm for the carb end would be my first thing to try. Go double the length at least, it will take that much to see any change. Otherwise it looks fine.

Give some thought to your off idle mixture too. I'm no expert on center mounted two barrels but it might be way too rich at that point in the curve. It sure was noticeable on my duals when I got it leaned out a bit on that end.
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PostPosted: Fri Jun 04, 2021 11:54 am    Post subject: Re: Morse Cable giving me the herky jerky Reply with quote

That setup is similar to my Chenowth with single HPMX 44. It's not overly touchy. Works fine and it too has a Morse cable.

I HATE to say it, but it might just be that you're not used to the touchy throttle and clutch, kinda like a kid learning to drive a manual transmission car. If you're used to driving an automatic or even many of the late model manual trans cars.

I'm finding that a LOT of people these days are not familiar with manual trans. My neighbor and someone on this forum were complaining recently that they had bought their teenager a manual trans car, then the professional driving instructors didn't know how to drive a stick.
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oprn
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PostPosted: Fri Jun 04, 2021 2:26 pm    Post subject: Re: Morse Cable giving me the herky jerky Reply with quote

Possible, not sure what the OP's previous driving experiance is but for my part I was practically born with a shifter in hand, have 55+ years of driving standards and my Manx copy was unmanageable. It could not be driven in 1st gear at steady "parking lot" speeds period! Nadda, no way! It's still a bit touchy by normal standards but definitely manageable by anyone but the greenest of stick drivers now.
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PostPosted: Mon Jun 07, 2021 7:27 am    Post subject: Re: Morse Cable giving me the herky jerky Reply with quote

dustymojave wrote:
I HATE to say it, but it might just be that you're not used to the touchy throttle and clutch, kinda like a kid learning to drive a manual transmission car. If you're used to driving an automatic or even many of the late model manual trans cars.


So your comment may have some legs to it, but not on the side of inexperience with a manual in general, as I've been driving stick for 20+ years. This could be a whole new beast as JimmyHoffa has mentioned to me, as I tend to drive with my toe or side of my foot, and not my heal. He has basically the identical set up and I encounter the same situation with his buggy.
Which tends to make me think I need to just change out the cable for a stock set up.

EDIT: Going to do some more experimenting with longer throttle arms and what have you first. Not going to just throw in the towel.
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skills@eurocarsplus wrote:
Shocked

that fucking thing looks like it drove through a J.C. Whitney catalogue and hit everything on the way out Laughing
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dustymojave
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PostPosted: Mon Jun 07, 2021 1:00 pm    Post subject: Re: Morse Cable giving me the herky jerky Reply with quote

So to follow the above, while trying to not offend...

If you have similar trouble with Jimmy's car, I know he's put in some comments regarding fixing the problem on your car, but has Jimmy driven yours and what is his take on the issue as a driver of your car?

Does Jimmy feel there is something wrong with the car? Or is it the newbie driver?

Note that I've seen this issue before with others who've found their buggy quite different from their BMW or Toyota pickup or whatever they've been driving on the street and have had some issues adjusting to it. As I've seen it, it was more of a matter of getting used to the car than fixing a problem.
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oprn
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PostPosted: Mon Jun 07, 2021 3:45 pm    Post subject: Re: Morse Cable giving me the herky jerky Reply with quote

Actually this is a common problem in production cars as well. Whenever the designer goes for more power by increasing the size of the carbs or FI butterfly there comes with it a non linear throttle response. There is a progression of the power band down the throttle opening scale. For instance if with an economy carb you get 50% power at 50% of the throttle travel and you increase that carb size or add more carbs of the same size the resultant throttle response may now be 50% power at 25% carb opening. The up side is that with the increase in carb size the engine flows fuel/air more freely and thus there is a small power gain at the top rpm too. Maybe 5 to 10%?

Add 2 more carbs or an even larger throttle body and now you might get another say 3 to 8% top rpm power? But the midrange has moved down once again so that you may be now getting 50% power at 15% open. The trade off for more power with a bigger and bigger carb/throttle body is a more and more non linear throttle response. Or a touchier and touchier gas peddle!

This is the big low end power boost that guys crow about with dual carbs on VWs! It's not really so much a power increase as it is a touchiness on the gas peddle.

So what do the car manufacturers do for this jack hammer tendency that comes with performance tuned engines?

Two things: First and most common is the progressive carb. Now you are essentially running two carb bores (4 on a V8 ) one for normal driving and one for spirited driving and they are linked together in such a way as to give a smooth "progression" from one to the other as the driving situation requires. It linearizes the throttle response and makes the engine more driver friendly. VW did this with their FI systems as well as the carbs on the water pumpers.

The second solution is to design a "progressive" linkage that opens the throttle plate slowly at first and more quickly as the throttle peddle is pushed further down. The most common approach to this is a cam shaped or offset wheel that the throttle cable runs in. The one on the FI throttle body of the Porsche 944 shows that very clearly. A very popular "power up grade" for the 944 is to replace that cam wheel with a round one which does absolutely nothing to increase power! Zero - zippo! It just makes the bottom end of the throttle feel touchy. Lots of guys like that... think it's the cat's a$$! Actually it is a design flaw and as you discovered a drivability problem.

You can try a few tuning things as I suggested with mixtures and timing and/or linkage changes. It made a big difference on mine. Most guys just learn to live with it and that's ok around town but on a long haul at light throttle the leg cramps from holding your foot in one position for hours get old quick, trust me!

Here is the Porsche solution and it works very well.

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I Ride Sand
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PostPosted: Sat Jun 12, 2021 10:56 pm    Post subject: Re: Morse Cable giving me the herky jerky Reply with quote

Has anyone bothered to ask/check to see if THE DRIVERS HEEL IS ACTUALLY BEING SUPPORTED?

if his heel is just sliding across the aluminum floor and not sitting on the bottom of the pedal, of course its going to be hard to get good throttle control! Go try to start out in your own buggy with your foot in the air not touching anything other than the top of the pedal/roller. My wife had the same issue driving my rail, I had to chuck a couple inches of foam behind her to make it so her heel was supported so it was drivable.

To the OP, try throwing some skate board grip tape on the floor. I saw that you have a full hinged pedal, does your heel sit against the bottom or do you have to "tip toe" the throttle?
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PostPosted: Mon Jun 14, 2021 8:30 am    Post subject: Re: Morse Cable giving me the herky jerky Reply with quote

I Ride Sand wrote:
To the OP, try throwing some skate board grip tape on the floor. I saw that you have a full hinged pedal, does your heel sit against the bottom or do you have to "tip toe" the throttle?


So to answer your question, yes, my heel is supported. We were able to remount the throttle pedal several inches closer to the driver seat to make up for my leg length. I can now (recently) firmly plant my heel into the pedal and rock my foot to apply throttle pressure, and now I can comfortable heel/toe when down shifting as well.
So again, it could just be an experience thing with a morse cable, as my other rail buggy has a roller pedal, and my beetle has a stock pedal set up. Either way, it's still annoying as hell.
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-76 Westy - "Gandalf"
-18 GTI SE

skills@eurocarsplus wrote:
Shocked

that fucking thing looks like it drove through a J.C. Whitney catalogue and hit everything on the way out Laughing
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oprn
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PostPosted: Mon Jun 14, 2021 8:37 pm    Post subject: Re: Morse Cable giving me the herky jerky Reply with quote

The battle is not lost yet. There are still a couple things to try.
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Aerindel
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PostPosted: Tue Jun 15, 2021 8:15 pm    Post subject: Re: Morse Cable giving me the herky jerky Reply with quote

I use a morse cable for my throttle...floor mount roller pedal....no jerky.

I do have some slack in the system and I've very carefully adjusted the cable to there is no tension on the carb when the pedal is release and about 1/8th play each way.
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