351 Glowing Header - Lame!
#1
09-07-2014, 01:21 AM
Join Date: Sep 2011
Location: Detroit, MI
Posts: 379
351 Glowing Header - Lame!
Right... so let me set the stage.
I've done all the smog deletes and installed a fmf q4 with the stock header and a mild grind on the inner header weld that seemed ever so restricting when I popped it apart originally, 101 webcam (valves shimmed this spring), 351 jug (of course!), K&N air filter no lid, 128 dyno jet, 3rd clip, 2.75 turns out "ish". Choke jet drilled .018 like the cool kids have done.
FYI I looked at the plug today and it had little or no story to tell, maybe a bit rich but no detonation for sure. Also all the research between here and other forums have me scratching my head so hence the post.
Few weeks back I rode the bike to a diaper party for one my bosses (felt awesome to finally get on the bike and feel the new engine since I've been working my life away all summer!).
Now let me explain the issue...
Everything was running fine all day... when I went to leave that night (dark out now) I started the bike with the choke on, I looked down after getting my gear on and noticed the pipe was glowing bright orange-red!!! quickly I pushed the choke in and the glow faded away to nothing. Wasn't too alarmed from this since this isn't unheard of. What was an issue is when I started cruising anything over 5.5k rpm "ish" the pipe would start to glow and increase in brightness until she was back to the bright orange-red at around 8k. Eventually I had to just baby it home at around 50mph since I didn't want to hurt anything.
Simply put I'm not sure how common this is, especially with proper air flow at higher speeds, and I know it may be hard for others to comment based on the extent of my mods...
Basically I'm going to change the main for starters, just not sure if I should start by going larger or smaller? In other words I can't really determine if this is a lean or rich issue... or maybe normal? Too many contradicting symptoms... if its rich like makes sense with the choke on then why does it happen at higher speeds with good air flow, when if anything it feels like it may be surging a tad bit at higher speeds indicating slightly lean.
I've done all the smog deletes and installed a fmf q4 with the stock header and a mild grind on the inner header weld that seemed ever so restricting when I popped it apart originally, 101 webcam (valves shimmed this spring), 351 jug (of course!), K&N air filter no lid, 128 dyno jet, 3rd clip, 2.75 turns out "ish". Choke jet drilled .018 like the cool kids have done.
FYI I looked at the plug today and it had little or no story to tell, maybe a bit rich but no detonation for sure. Also all the research between here and other forums have me scratching my head so hence the post.
Few weeks back I rode the bike to a diaper party for one my bosses (felt awesome to finally get on the bike and feel the new engine since I've been working my life away all summer!).
Now let me explain the issue...
Everything was running fine all day... when I went to leave that night (dark out now) I started the bike with the choke on, I looked down after getting my gear on and noticed the pipe was glowing bright orange-red!!! quickly I pushed the choke in and the glow faded away to nothing. Wasn't too alarmed from this since this isn't unheard of. What was an issue is when I started cruising anything over 5.5k rpm "ish" the pipe would start to glow and increase in brightness until she was back to the bright orange-red at around 8k. Eventually I had to just baby it home at around 50mph since I didn't want to hurt anything.
Simply put I'm not sure how common this is, especially with proper air flow at higher speeds, and I know it may be hard for others to comment based on the extent of my mods...
Basically I'm going to change the main for starters, just not sure if I should start by going larger or smaller? In other words I can't really determine if this is a lean or rich issue... or maybe normal? Too many contradicting symptoms... if its rich like makes sense with the choke on then why does it happen at higher speeds with good air flow, when if anything it feels like it may be surging a tad bit at higher speeds indicating slightly lean.
Last edited by LikesToThump; 09-07-2014 at 01:24 AM.
#2
09-07-2014, 01:42 AM
Join Date: Jan 2013
Location: Las Vegas, NV
Posts: 1,422
Huh, I had the same jetting, save for the choke jet mod, at 2.2k elevation, never experienced glowing header before. Clogged jet perhaps? causing to run too lean?
#3
09-07-2014, 11:53 AM
At your elevation, a fully modded stock bore (like mine - see my sig line) needs the DJ 132 and needle clip set one notch lower than Stage 2 to get below 15:1 AFR - which is still too lean.
Just FYI..
Just FYI..
#4
09-07-2014, 01:13 PM
This chart was at a Blacksmith site and likely matches up with any materials characteristics chart for the same. I remember using color for tempering in some metal work we did in the basic metals class for Industrial Arts ed. Figured it would give a fair gauge for your header temperature.
Figure the single wall exhaust is going to run hot and glow when sitting still, exhaust gasses run up around 1500-1700 deg F. I can't say for the moving part, I'd think the pipe would cool below a glowing point.
You can compare what you saw to this chart to have an idea of the metal temperature. As you see, the glow can start at a fairly low temperature, but glowing like you described when moving seems a bit hot. So here are some thoughts.
From what I've understood with two strokes, but not positive it is correct for four strokes, too rich and too lean can both run hot. But I'm thinking, again not a fact, if you still have the air suction pollution system it could make the glow happen under rich conditions, burning the unburnt mix in the pipe itself raising the temperature there. Too lean just plain runs hot exhaust gasses and might make the header glow, but still in the wind it should not be too bright.
I will say with the Mikuni enrichener as a choke you can test your jetting when there's a surge. Opening the enrichener will add slightly, making the mix slightly richer. If your surge goes away a bit, the mix is lean. No effect will likely mean it is right or rich.
If your plug check for a constant long run in that range shows good on jetting you should not hurt a thing... well, if you touch the exhaust you'll burn yourself, but the engine should be doing fine inside. If it was too hot the electrode would show it. Exhaust can run up to around 1600 deg F according to this discussion on typical gasoline exhaust temps in The Diesel Stop forum, with one commentator running dynos frequently and working for one of the big three. It rings pretty true from what I've understood in the past.
Now I want to go run my 250 in the dark to see if the pipe glows!
Figure the single wall exhaust is going to run hot and glow when sitting still, exhaust gasses run up around 1500-1700 deg F. I can't say for the moving part, I'd think the pipe would cool below a glowing point.
You can compare what you saw to this chart to have an idea of the metal temperature. As you see, the glow can start at a fairly low temperature, but glowing like you described when moving seems a bit hot. So here are some thoughts.
From what I've understood with two strokes, but not positive it is correct for four strokes, too rich and too lean can both run hot. But I'm thinking, again not a fact, if you still have the air suction pollution system it could make the glow happen under rich conditions, burning the unburnt mix in the pipe itself raising the temperature there. Too lean just plain runs hot exhaust gasses and might make the header glow, but still in the wind it should not be too bright.
I will say with the Mikuni enrichener as a choke you can test your jetting when there's a surge. Opening the enrichener will add slightly, making the mix slightly richer. If your surge goes away a bit, the mix is lean. No effect will likely mean it is right or rich.
If your plug check for a constant long run in that range shows good on jetting you should not hurt a thing... well, if you touch the exhaust you'll burn yourself, but the engine should be doing fine inside. If it was too hot the electrode would show it. Exhaust can run up to around 1600 deg F according to this discussion on typical gasoline exhaust temps in The Diesel Stop forum, with one commentator running dynos frequently and working for one of the big three. It rings pretty true from what I've understood in the past.
Now I want to go run my 250 in the dark to see if the pipe glows!
Last edited by klx678; 09-07-2014 at 01:23 PM.
#6
09-12-2014, 01:07 AM
Join Date: Sep 2011
Location: Detroit, MI
Posts: 379
This chart was at a Blacksmith site and likely matches up with any materials characteristics chart for the same. I remember using color for tempering in some metal work we did in the basic metals class for Industrial Arts ed. Figured it would give a fair gauge for your header temperature.
Figure the single wall exhaust is going to run hot and glow when sitting still, exhaust gasses run up around 1500-1700 deg F. I can't say for the moving part, I'd think the pipe would cool below a glowing point.
You can compare what you saw to this chart to have an idea of the metal temperature. As you see, the glow can start at a fairly low temperature, but glowing like you described when moving seems a bit hot. So here are some thoughts.
From what I've understood with two strokes, but not positive it is correct for four strokes, too rich and too lean can both run hot. But I'm thinking, again not a fact, if you still have the air suction pollution system it could make the glow happen under rich conditions, burning the unburnt mix in the pipe itself raising the temperature there. Too lean just plain runs hot exhaust gasses and might make the header glow, but still in the wind it should not be too bright.
I will say with the Mikuni enrichener as a choke you can test your jetting when there's a surge. Opening the enrichener will add slightly, making the mix slightly richer. If your surge goes away a bit, the mix is lean. No effect will likely mean it is right or rich.
If your plug check for a constant long run in that range shows good on jetting you should not hurt a thing... well, if you touch the exhaust you'll burn yourself, but the engine should be doing fine inside. If it was too hot the electrode would show it. Exhaust can run up to around 1600 deg F according to this discussion on typical gasoline exhaust temps in The Diesel Stop forum, with one commentator running dynos frequently and working for one of the big three. It rings pretty true from what I've understood in the past.
Now I want to go run my 250 in the dark to see if the pipe glows!
Figure the single wall exhaust is going to run hot and glow when sitting still, exhaust gasses run up around 1500-1700 deg F. I can't say for the moving part, I'd think the pipe would cool below a glowing point.
You can compare what you saw to this chart to have an idea of the metal temperature. As you see, the glow can start at a fairly low temperature, but glowing like you described when moving seems a bit hot. So here are some thoughts.
From what I've understood with two strokes, but not positive it is correct for four strokes, too rich and too lean can both run hot. But I'm thinking, again not a fact, if you still have the air suction pollution system it could make the glow happen under rich conditions, burning the unburnt mix in the pipe itself raising the temperature there. Too lean just plain runs hot exhaust gasses and might make the header glow, but still in the wind it should not be too bright.
I will say with the Mikuni enrichener as a choke you can test your jetting when there's a surge. Opening the enrichener will add slightly, making the mix slightly richer. If your surge goes away a bit, the mix is lean. No effect will likely mean it is right or rich.
If your plug check for a constant long run in that range shows good on jetting you should not hurt a thing... well, if you touch the exhaust you'll burn yourself, but the engine should be doing fine inside. If it was too hot the electrode would show it. Exhaust can run up to around 1600 deg F according to this discussion on typical gasoline exhaust temps in The Diesel Stop forum, with one commentator running dynos frequently and working for one of the big three. It rings pretty true from what I've understood in the past.
Now I want to go run my 250 in the dark to see if the pipe glows!
. Yes by all means it was in the middle upper range... 1800 or more ish. Opening up the choke at cruise speed is a great idea and I can't believe I didn't think of it sooner! (maybe because initially the choke made it glow or something lol)
I get a few days off finally and I'm going to test it out this weekend, I'll do my best with pics to post.
#7
09-12-2014, 01:11 AM
Join Date: Sep 2011
Location: Detroit, MI
Posts: 379
Ppl were preaching the 128 on a thread here back when I was starting the big bore project in my living room last winter... that's kinda why I kept it so low on the numbers. After a few tests this weekend I think I'll try some jetting closer to yours.
#8
09-12-2014, 05:25 AM
Well you can't blame anyone for the lean jetting advice - they just didn't know better. Fact is my bike ran great with the #128. I would never have known how lean the bike was if it wasn't for my first dyno test. As far as I can tell, I'm the only one to have complete Dynojet Dyno charts to verify HP, TRQ and AFR, on our mods, on a stock bore, in our forum. I don't pretend to know what happens when you have a 351BB sucking thru a CV34 but if it were a 250.... I'll go ahead and guess that there is no way to properly fuel the 351 , near sea level, with the DJ kit. I would order #134,#136,and #138 DJ main jets - put in the 136 and dyno.
BTW, I picked up over 1hp, just with the jetting change, over the Stage 2 with #128 setup. Perhaps your in for an even more pleasant surprise.
BTW, I picked up over 1hp, just with the jetting change, over the Stage 2 with #128 setup. Perhaps your in for an even more pleasant surprise.
Last edited by Klxster; 09-12-2014 at 05:27 AM.
#9
09-12-2014, 12:36 PM
Just to play the contrarian, my 331 with the #132 jet was pig rich. So bad in fact that the bike wouldn't even pull to redline WOT in 3rd or 4th even with the airbox lid removed. I had to go back to the #128, which is the same as I had on the bike when it was still a 250. The extra air moving with the big bore kit may be increasing the amount of fuel through the venturi of the carb and negates the need for a bigger jet ?
I don't pretend to be an expert and I have no AFR readings to back anything up, but I know what a rich condition feels like and the #132 was way to big for me. I'm at 1,300 ASL FWIW.
YMMV
I don't pretend to be an expert and I have no AFR readings to back anything up, but I know what a rich condition feels like and the #132 was way to big for me. I'm at 1,300 ASL FWIW.
YMMV
