pogging & huvering RPM

jazzyrigged · Posted: August 16, 2006, 2:44 pm Post subject: pogging & huvering RPM

Perhaps someone can help me with this problem before I become psychotic Twisted Evil

with it all. The problems I am having with my 78 special are as follows:

1) When running {either at idle or during normal driving conditions} I keep hearing a "pogging" sound. It sounds as if it is either not fully combusting, or not combusting at all. I have also noticed a low "popping" sound coming from the carbs. When this happens the carbs "dance" ever so slightly.

2) When the engine is hot {particularly during hot weather in St. Louis} the engine idle climbs and hovers at about 4000 RPM's. Adjusting the engine idle screw seems to help, but this is too much of a pain in the posterior to do while riding, and very annoying as well.

3) At times the engine will drop gradually in RPM's until it totally kicks out and then is difficult to restart.

Any ideas or suggestions would be much appreciated.

bigj8550 · Posted: August 16, 2006, 3:11 pm Post subject: Re: pogging & huvering RPM

definaly sounds like a carb issue to me! In fact mine did the same thing. To fix my issue I tore down and cleaned and put in new needle and seats. Then I sync the carbs the bike runs great now. Do it all at once trust me don't try to side skirt and do a small fix go through the carbs and replace any thing you can find that needs to be replaced. pay close attention to the rubber diaphrams with the needle slides on them. I know at 69.00 a pop from mikes xs they are a little pricey but if you need them then replace them. To sync the carbs build yourself a 3.00 manometer I will try to find a link to it. all it is a aquaum tubing trans fluid tape and a yard stick. Laughing

Don't laugh it works! If you do this then your bike will give years of more serivce.

jazzyrigged · Posted: August 16, 2006, 3:54 pm Post subject: Re: pogging & huvering RPM

would I be best off getting a rebuild kit from mikesxs?

bigj8550 · Posted: August 16, 2006, 4:06 pm Post subject: Re: pogging & huvering RPM

So far that is where I have bought most of my parts. I only go to the dealer if mikes doesn't have it. I found the link for the home made manometer
www.powerchutes.com/manometer.asp
try that it worked for me. Very Happy

5twins · Full Member Joined: Aug 05, 2006 Posts: 1616

jazzyrigged · Posted: August 17, 2006, 10:58 am Post subject: Re: pogging & huvering RPM

O.K I feel a little like a rube, but I'm not sure where to connect the ends of the manometer on the carbs. Great link, shows just how to build it.

kingwj · Posted: August 17, 2006, 12:50 pm Post subject: Re: pogging & huvering RPM

Later bikes had a tap off the carb mounts. My bike uses it for the vacuum petcocks. Later bikes just capped them off. This is where the manometer would typically be mounted. If you don't have the vacuum taps I am at a loss on where you would hook up the manometer. In this case a uni-syn would work. You can also stick a piece of tubing in the carb and listen to the sound. First thing is to disconnect the linkage between the carbs so you can adjust them independently. Adjust so they make the same pitch sound. You can get quite close using this method.

KYLEPRESTON · Posted: August 17, 2006, 1:28 pm Post subject: Re: pogging & huvering RPM

SO HOW ARE THOSE CARBS DOING?

5twins · Full Member Joined: Aug 05, 2006 Posts: 1616

jazzyrigged · Posted: August 18, 2006, 8:54 am Post subject: Re: pogging & huvering RPM

Update: Lubed the ATU and nothing significant happened. I think the next course of action will be to order a set of rebuild kits and perhaps some new springs for the ATU.

Thanks for everybody's input on the matter. It truly has been quite helpful. Any further suggestions would also be highly appreciated. Hopefully by next week I may be up and running again.

xsjohn · Posted: September 3, 2006, 3:43 pm Post subject: Re: pogging & huvering RPM

Choke problems! Look on the engine side of the butterfly and you will see a large hole. This leads air to choke. If choke is balled up it will raise rpms. I havn't ever fixed one but my friend has that problem on both of his 38nn's.
Hope this helps. John Underwood Old Yamaha mechanic.

Jack · Full Member Joined: Mar 15, 2005 Posts: 411

Did you completetly disassemble the centrifugal weight assembly for proper cleaning and lubing of the cam end bushings that support the advance rod? I 've heard rummors regarding the replacements ATC spring tensions are weak not allowing the ignition advance to retard at idle.A simple solution would of been to cut one coil off the original springs........Jack

jkoz · Posted: September 12, 2006, 8:47 am Post subject: Re: pogging & huvering RPM

Hmm... Sounds exactly like the problem I am having. Popping on the low end and floating idles. Guess I need to rebuild. Is the rebuild kit the best way to proceed?

Also I was thinking about getting the K&N RC-0982 air filters as well. How tough is it usually to the a bike propperly rejetted after changing filters? This is something that I have never had to do.

5twins · Full Member Joined: Aug 05, 2006 Posts: 1616

jkoz · Posted: September 13, 2006, 12:36 am Post subject: Re: pogging & huvering RPM

My bike is an '83 Heritage Special. Just recently picked it up so I am still working out what exactly needs to be done to it and what has been done.

I haven't looked in detail, but I am pretty sure that the lead plug hasn't been removed yet. It will be next week though, have a week off of work and hoping to do some of the primary performance changes that I keep seeing mentioned on the forum.

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